Biden: Cost to Russia will rise if its Ukraine aggression persists

US Vice President Joe Biden warned Moscow on Tuesday that Western pressure will only harden if Russia' "aggression" against neighbouring war-scarred Ukraine persists.

"If Russian aggression persist, the cost imposed on Moscow will continue to rise," Biden said in a rare appearance by a top Western official before the Ukrainian parliament.

"The US will maintain pressure until Moscow fulfils its (peace deal) commitments," he said. "Despite some de-escalation in violence, there can be no sanctions relief unless and until Russia meets all of its commitments under the (February) Minsk agreements."