US Vice President Joe Biden said Monday that Washington remained determined to see Russia adhere to a shaky Ukrainian peace agreement and hand back Crimea to Kiev.

US Vice President Joe Biden said Monday that Washington remained determined to see Russia adhere to a shaky Ukrainian peace agreement and hand back Crimea to Kiev.

Biden's visit is his fourth to Kiev since Russia annexed Ukraine's Black Sea peninsula following national referendum in March 2014.

"The US stands firmly with the people of Ukraine in the face of continued, I emphasize, continued aggression from Russia and Russian-backed separatists," he told Ukrainian President Poroshenko.

"The invasion by Russia of Crimea will not be accepted by us or by the international community. This attempted annexation is contrary to international law, is wrong, and will not be accepted in any circumstance," he said.

Biden also hinted that Russia may face additional US sanctions if its “peace commitments were not met.”

Washington was in contact with "our fellow leaders around the world... to make sure the international community stands and holds Russia accountable for the actions against Ukraine," Biden said after meeting with Ukrainian Prime Minister Arseniy Yatsenyuk.

"If they do not meet their obligations, (one must) increase the price Russia has to pay for its illegal actions internationally."