US President Joe Biden, 79, warned Russia was now likely to invade nearby Ukraine. Speaking at a news conference to mark his first year in office on Wednesday, he said: “I’m not so sure he is certain what he is going to do.
“My guess is he will move in. He has to do something.”
Mr Biden added: “He is trying to find his place in the world between China and the west.”
The 46th President’s comments come as 100,000 Russian troops are stationed close to the Ukrainian border.
However, the Kremlin has denied it is planning to launch an attack against Kyiv.
Russia annexed the Crimean peninsula back in 2014 after Ukraine’s pro-Moscow Government was overthrown.
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There are now growing concerns the conflict, which is estimated to have cost at least 13,000 lives, could return amid growing tensions.
Mr Biden also suggested Vladimir Putin, 69, was fully aware of the consequences of military intervention.
The 46th President, who held talks with his Russian counterpart last month, said: “Do I think he’ll test the West?
“Test the United States and NATO as significantly as he can?
“Yes, I think he will but I think he’ll pay a serious and dear price for it.”
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However, Mr Biden faced criticism from an official in Kyiv after he suggested a “minor incursion” would not result in the same retaliatory measures.
The official told CNN: “This gives the green light to Putin to enter Ukraine at his pleasure.”
The American Secretary of State Antony Blinken, 59, echoed Mr Biden’s comments during a visit to Kyiv by suggesting Russia could attack “on very short notice”.
Mr Blinken is set to meet with Russia’s Foreign Minister Sergei Lavrov, 71, in Geneva on Friday.