New satellite imagery showing Russian President Vladimir Putin amassing troops and resources on the Russia-Ukraine border is sparking fears of an invasion of the former Soviet state, with the possibility of war being a likely byproduct of President Biden's perceived weakness on the world stage, according to retired Army Gen. Jack Keane,

Keane, a former vice chief of staff of the U.S. Army under Presidents Bill Clinton and George W. Bush, told Fox News host Martha MacCallum that Russia is "absolutely poised" to attempt a military invasion of Ukraine – after forcibly annexing its Crimea region during the Obama years.

"We’ve been tracking this at the Institute for the Study of War now for a couple of months. They have finally moved in the artillery units, logistical infrastructure, major command headquarters that they would need to sustain an invasion. So he’s poised to do that," Keane said on Monday's installment of "The Story." 

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With neighboring Belarus being controlled by authoritarian President Alexander Grigoryevich Lukashenko, Keane suggested Moscow might call on the country to accommodate additional troops, giving the ex-KGB agent even more breadth along the Ukrainian border.

Russia's President Vladimir Putin addresses the media during a press conference after the U.S.-Russia summit with U.S. President Joe Biden at Villa La Grange in Geneva, Switzerland, Wednesday, June 16, 2021. (Denis Balibouse/Pool Photo via AP) (Denis Balibouse/Pool Photo via AP)

Belarus, Keane noted, also shares a border with NATO-member Poland, which would complicate matters, he claimed.

"The other option certainly is just take control of the country, go in to the unoccupied spaces, so to speak where there’s no conflict taking place and go for Kiev. That I think is unlikely," he said.

Putin might not go that extreme route because it could bog the Russians down in an extended conflict "for decades", he said.

President Biden is scheduled to talk with Putin Tuesday to discuss the unfolding situation. 

"This meeting [between Putin and] President Biden is very important, because I’m convinced that the reason why we have acceleration from China, from Iran and from Russia [is] there’s a perception that this presidency and this administration is more about accommodation and appeasement than about confronting and countering the strategic objectives of these three adversary countries," Keane added.

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"People may disagree with the rhetoric associated with [Trump], but the policies were firm. Our adversaries understood that. I believe the reason for this is they see weakness here," he said. "I don’t like saying that, but that is the conclusion one must draw in terms of what is happening here."

Keane added that the amassing of troops on the Ukrainian border is only one aspect of Putin's increasingly confrontational behavior – pointing ot how he is "enabling" Lukashenko to escalate its own behavior toward Poland in the form of "weaponizing migration" – as well as building leverage over Europe's energy supply.

Belarusian President Alexander Lukashenko speaks during a meeting with Commonwealth of Independent States officials in Minsk on May 28, 2021.  (DMITRY ASTAKHOV/POOL/AFP via Getty Images)

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Keane offered his advice on what the Biden administration should have done throughout the year. 

"What [the U.S.] should have done early in the year when Putin began to get more aggressive with Belarus and began to get more aggressive with moving troops in to the vicinity of the Ukraine, we should have moved NATO forces in to Poland and make certain that Putin is getting the message that we’re not going to permit any undermining of NATO," he said. "We should have put a large package of lethal weapon capability in to Ukraine. We gave them some things, but nowhere near what they’re asking for in terms of lethality that makes a difference if Putin comes in. That’s something that his leaders would pay attention to."