The head of NATO on Thursday called on Russia to withdraw the estimated 20,000 troops massed along the Ukrainian border, amid fears that Moscow may invade its neighbor.
"I call on Russia to step back from the brink, step back from the border and not use peacekeeping as an excuse for war-making," NATO Secretary General Anders Fogh Rasmussen said during a visit to Ukraine, according to Reuters.
In a phone call Wednesday, Vice President Biden and Ukrainian President Petro Poroshenko also discussed the troop buildup.
In the spring Russia had sent 40,000 troops to the border, drawing that number down to 1,000 in June. But after being hit with new Western sanctions over its continued support for rebels in eastern Ukraine, Moscow raised troop levels to 20,000 and moved them closer to the border.
Top Pentagon spokesman Rear Adm. John Kirby on Tuesday scolded Russia, saying that the buildup was "doing nothing but continuing to escalate the tension that exists inside eastern Ukraine."
Rasmussen on Thursday also charged Russia with ramping up support for separatists in Ukraine, who are suspected of downing a passenger jet last month.
The rebels have set up a recruitment office in Moscow and are openly seeking more fighters from within Russia's capital, USA Today reported Thursday.
In a separate news conference on Thursday, Rasmussen warned that the West would deliver "deeper, more profound, tougher sanctions" on Russia if the country continues supporting military proxies, according to the Kyiv Post.