Lt. Gen. Keith Kellogg told Fox News that there's "not much" President Biden can do to stop a bigger invasion of Ukraine by Russia.

Russian President Vladimir Putin said that he is green lighting a "special military operation" in Ukraine on early Thursday morning local time, and said that "Russian President Vladimir Putin "our confrontation with these [Ukrainian] forces is inevitable."

This was followed by explosions heard across Ukraine, in Kyiv, Kharkiv, Odessa, and more cities.

PUTIN DECLARES 'SPECIAL MILITARY OPERATION' IN UKRAINE: LIVE UPDATES

Vladimir Putin

Russian President Vladimir Putin gestures while speaking to the media during a joint news conference with Hungary's Prime Minister Viktor Orban following their talks in the Kremlin in Moscow, Russia, Tuesday, Feb. 1, 2022. Putin says the U.S. and its allies have ignored Russia's top security demands. In his first comments on the standoff with the West over Ukraine in more than a month, Putin said Tuesday that the Kremlin is still studying the U.S. and NATO's response to the Russian security demands received last week. (Yuri Kochetkov/Pool)

"Well, unfortunately there's not much [President Biden] can do," Kellogg said. "We're not going to put troops in Ukraine. Ukraine is not a member of NATO."

Kellogg said that President Biden "must" rally all of NATO and the rest of the world. 

"And now, it's time to rally the world, because there's not much he can do physically in Ukraine, because they're not a NATO ally." Kellogg said.

BIDEN RESPONDS TO RUSSIA'S INVASION OF UKRAINE: 'THE WORLD WILL HOLD RUSSIA ACCOUNTABLE'

President Joe Biden

FILE = This image provided by The White House via Twitter shows President Joe Biden at Camp David, Md., Feb. 12, 2022. A new poll finds little support among Americans for a major U.S. role in the Russia-Ukraine conflict. President Joe Biden has acknowledged the growing likelihood of a new war in Eastern Europe will affect Americans even if U.S. troops don’t deploy to Ukraine. Just 26% of Americans say the U.S. should have a major role in the conflict between Russia and Ukraine, according to a new poll from The Associated Press-NORC Center for Public Affairs Research. (The White House via AP, File)

Ukrainian Minister of Foreign Affairs said on early Thursday morning in Ukraine that Putin has launched a "full-scale invasion" of Ukraine.

Kellogg warned that the situation in Ukraine will be "incredibly changing," and said that there may not be concrete answers soon.

"It's going to be very, very chaotic, and you just have to live with it," Kellogg said.

He added that it's still early morning in Ukraine, stating that "the first stages of any military operation are always a little bit chaotic for everybody."

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Ukrainian President Volodymyr Zelenskyy answers questions from the media in Kyiv, Ukraine, on Friday.

Ukrainian President Volodymyr Zelenskyy answers questions from the media in Kyiv, Ukraine, on Friday. (Ukrainian Presidential Press Office/AP)

At this point, Kellogg says the biggest question is just how far Putin is willing to go.

"The biggest thing, I think the biggest question you want answers to is how large of an invasion is this? Is he looking at taking Odessa in the south? Is he looking to take Kyiv?," Kellogg said. "These are the things you're going to have to watch for to get indicators from.