Ukraine war latest updates: Russia launches surprise advance on Ukraine - but why has Moscow opened up second front in war?

Volodymyr Zelenskyy has issued an updated statement on the situation in Kharkiv. 

In a post on Telegram, the Ukrainian president said Russian troops have tried to expand their operations. 

But he added that Ukraine understands the "scope of the occupier's forces". 

"We see his plan," he said. "Our soldiers, our artillery, our drones respond to the occupier." 

He also said Ukrainian forces were adding their "strength" along the state border and the entire frontline near Kharkiv. 

"We will invariably destroy the occupier in such a way as to thwart any Russian offensive intentions," the 46-year-old leader wrote. 

"Everything depends on the stability of our soldiers, and everyone who holds a position now protects the position of all of Ukraine.

"It is important that partners support our soldiers and Ukrainian stability with timely supplies. Really timely. The package that really helps is the weapons brought to Ukraine, not just the announcement of the package." 

Volodymyr Zelenskyy has thanked Joe Biden after a $400m military aid package was announced by the US. 

The Ukrainian president said the assistance will "help save civilian lives" and strengthen troops on the frontline. 

"The United States maintains its leadership role in supporting Ukraine and this has historic significance," he added. 

This is the third tranche of aid for Ukraine since Congress passed supplemental funding in late April after months of gridlock.

The package includes: 

• High Mobility Artillery Rocket Systems and rockets for them
• Munitions for Patriot and National Advanced Surface-to-Air Missile Systems
• Artillery
• Anti-aircraft and anti-tank munitions
• An array of armoured vehicles, such as Bradley and Mine Resistant Ambush Protected vehicles
• Coastal and riverine patrol boats
• Trailers
• Demolition munitions
• High-speed anti-radiation missiles
• Protective gear, spare parts and other weapons and equipment

The weapons are being sent through presidential drawdown authority, which pulls systems and munitions from existing US stockpiles so they can go quickly to the war front. 

By Deborah Haynes, security and defence editor, in Vovchansk

Terror and grief were the overwhelming emotions from dozens of mainly elderly men and women who fled the Ukrainian border town of Vovchansk after Russian forces attacked.

Gathered at an evacuation point just outside the town, they said it had been the fiercest fighting they had ever experienced since the full-scale invasion.

Sky News followed a pair of volunteer rescuers, who drove a white van into the tow to help residents evacuate.

Smoke hung over the road on the way – we were told all roads into Vovchansk were being targeted by Russian artillery, rockets and drones.

One of the attacks had ignited a fire in a forest that lined the road, sending clouds of smoke into the air.

The streets of the part of the town we entered were almost completely empty.

We pulled into a residential area of bungalows.

A group of five elderly men and women sat or stood on a bench on the side of the road, seemingly happy to stay put.

The rescue team pulled up outside an address where they had been told four residents wanted to be evacuated.

They knocked on the door, but no one replied. Instead, a petite, grey-haired woman who lives in the next door house pushed open her green gate and told the rescuers that her neighbours had already gone.

Distraught, Valentina, 74, had no plans to leave, but the rescuers managed to persuade her.

"Let's go, don’t stay here, it is dangerous," they said.

Suddenly there was a boom – it seemed to change her mind.

Gathering a few simple belongings, she was led out of her home and into the minibus.

The mayor said some 500 people from the town have been evacuated since the attack began, but he said the town’s population was 3,000, with many more yet to leave.

Evacuation operations are set to continue.

By Sean Bell, military analyst 

At 5am, the Russians launched a surprise attack on the Kharkiv region of northeastern Ukraine, killing two civilians and injuring at least five others. 

The Ukrainian border community of Vovchansk was one of the targets - this community is only 5km away from the Russian border, and the attack led to the evacuation of 3,000 residents. 

Russian forces are reported to have advanced around 1km, before Ukrainian reinforcements were deployed.

So why has Russia opened up a second front in the war?

There are probably two key reasons for this latest Russian attack.

First, the Russian border town of Belgorod is a logistics hub for Russian military activity, and is regularly targeted by artillery from Ukrainian territory.

President Putin has long promised to create a buffer zone to push Ukrainian forces out of artillery range, which would limit the attacks on this frontier town. 

Secondly, although most analysts believe Russia would struggle to seize Kharkiv, the attack does force Ukraine to spread its limited resources across a broader front, leaving it more vulnerable to further attacks.

Russian's priority still appears to be the Donbas - a primary objective of what it calls its special military operation. 

Russia's military are evidently exploiting the window of opportunity created by Ukraine's current shortage of weapons, and are reported to be preparing for a major summer offensive. 

Ukraine's strategy appears to be to trade territory for time, making Russia pay a high price for every metre of ground seized, pending the arrival of the West's next delivery of military aid.

But, momentum and initiative are vital commodities in war, and Russia has both at this crucial juncture.  Ukraine is on the back foot, and could face a very difficult next few weeks on the battlefield.

The UK's foreign secretary, Lord Cameron, said last week Ukraine has a right to use British-supplied weapons against targets inside Russia.

Referring to those comments, senior Russian security official Dmitry Medvedev warned the West against greenlighting Ukrainian attacks on its territory using Western-supplied weapons.

After what Moscow said were threats from France, Britain and the US, Russia said earlier this week it would practise the deployment of tactical nuclear weapons as part of a military exercise.

These exercises are to work out Russia's response to any attacks on the country using weapons supplied by the West, Mr Medvedev claims.

He said the Russian response would "be aimed not only at Kyiv" - and took personal aim at Lord Cameron.

"I remember this guy quite well. I worked with him when he became prime minister. An ordinary dull Brit. At that time, he was joyfully stupid and looked like a young devil who was revelling in his unexpectedly acquired position," he wrote on the Telegram messaging app, which has been translated.

"Under certain circumstances, the response [to such attacks] will be aimed not only at Kyiv," he added.

He added: "And not just with conventional explosives, but also with a special kind of arms."

As we have been reporting throughout the day, Russian forces gave started the first stage of an operation in Kharkiv. 

Fierce fighting has been taking place in parts of the northeastern region, and Ukrainian officials have claimed Russian troops have advanced by 1km. 

Leading US thinktank the Institute for the Study of War has said evidence indicates the initial Russian attacks have been carried out for reconnaissance and not as a major drive to seize Kharkiv city. 

It has also suggested five objectives Russia might be trying to achieve with the operation: 

1. To thin out Ukrainian forces along the 600-mile frontline, and create opportunities in Donetsk in eastern Ukraine.
2. Draw Ukraine forces towards Vovchansk in Kharkiv to facilitate Russia's efforts to seize Kupyansk - another city in Kharkiv. 
3. Create a demilitarised or sanitary buffer zone in Ukraine.
4. Instil panic in Ukraine.
5. Set conditions for a larger future offensive on Kharkiv. 

The ISW added that Russia was unlikely to take control of Kharkiv city. 

Open source data suggests Moscow's forces have an insufficient number of troops in nearby areas to seize it, the thinktank added. 

"If the Russian command intended to seize Kharkiv city, then Russian forces would have likely also attacked to the west and northwest of Kharkiv city as well," it said. 

It also explained that Russia's use of its airspace for the Kharkiv attacks highlights the "urgent need" for the US to provide more long-range air defences to Ukraine. 

"Ukraine would be better able to defend Kharkiv oblast if Ukrainian air defenders could intercept Russian aircraft in Russian airspace before they drop their glide bombs," it added.

Although there is growing expectation that the initial tranche of F-16 fighter jets being donated to Ukraine could arrive as soon as early July (see our 3.50pm post), it is not clear when the other ingredients of this powerful air power capability will be in place by that time.

Providing a credible and effective Ukrainian combat air capability requires suitably trained and experienced pilots, groundcrew, weapons, defensive aids and radar.  

All these components need to be in place before the Ukrainian air force will be ready to go into battle with the Russian military. 

Once the F-16s are place, the challenge facing Ukraine will be when and where to use these valuable resources - and how to avoid them being destroyed before they can contribute to the Ukrainian defensive effort.

When the F-16s arrive, they will provide Ukraine with an invaluable - albeit scarce - resource. 

They could be used to support the frontline, but they will be very vulnerable in that dynamic and hostile air environment.

They could also be used to conduct strikes against key Russian military targets inside Russian territory, which would certainly force a change in Russian tactics.

Or, if Ukraine wanted to threaten Crimea, the F-16s could be used in a co-ordinated attack in support of a wider campaign.

Regardless, with Russia on the front-foot in the Donbas, Ukraine needs all the help it can to reverse Russian momentum on the battlefield.

If you're just joining us, here's a recap of the key developments so far today: 

• Volodymyr Zelesnkyy says fierce fighting is ongoing in the Kharkiv region as a Ukrainian official claims Russian troops have advanced 1km in their attempt to create a buffer zone;
• Civilians have been evacuated from the town of Vovchansk, in Kharkiv, where Russian shelling is said to be intense;
• In a separate overnight attack on Kharkiv, two civilians have been killed and another five injured, according to the region's governor;
• Ukraine says it expects to receive the first F-16 fighter jets this summer;
• Vladimir Putin's pick for prime minister was waved through parliament unopposed as he begins his new six-year term as president;
• Moscow's mayor says anti-aircraft units intercepted a drone over the south of the city early this morning.

Vladimir Putin's pick for prime minister has been confirmed, as expected, after the nomination was swiftly waved through parliament.

Today, Mr Putin proposed the reappointment of Mikhail Mishustin (see our 9.17am post), a technocrat who has helped him through the war in Ukraine and the economic challenges posed by the subsequent Western sanctions.

The Duma, the lower house of Russia's parliament, approved his nomination on the same day.

There is virtually no opposition in the Russian parliament, which has supported Mr Putin in all his decisions, including the February 2022 invasion of Ukraine.

Deputies from the opposition Communist party abstained from voting.

The US is putting together a $400m (£320m) military aid package for Ukraine, an official has told the Reuters news agency.

Speaking anonymously, the official said the aid includes artillery, anti-tank munitions, armoured vehicles and small arms that can be used immediately on the battlefield.

The move suggests the US is returning to a regular pace of supplying weapons to Ukraine, following the passage of a $60bn bill.