KIEV - US Vice President Joe Biden warned Russia on Tuesday that Western pressure on Moscow would only increase if Russian "aggression" against neighbouring war-scarred Ukraine continued.

"If Russian aggression persists, the cost imposed on Moscow will continue to rise," Biden said in a rare address by a top Western official to the Ukrainian parliament on the second day of a visit to Kiev.

"The US will maintain pressure until Moscow fulfils its Minsk commitments," he said, warning there would be "no sanctions relief" until Russia fully implemented its end of a peace deal signed in the Belarussian capital Minsk in February.

The tough message flew in the face of the Kremlin's assertion that it is Ukraine's pro-Western leadership that keeps flouting the accord aimed at ending 19 months of fighting with pro-Russian rebels that has claimed more than 8,000 lives.

Biden's trip was his fourth to Kiev since Russia annexed Ukraine's Crimea peninsula in March 2014 and then watched with approval as pro-Kremlin fighters carved out their own region in the east of the ex-Soviet state.

Both Washington and Brussels have slapped economic sanctions on Russian President Vladimir Putin's inner circle and have helped train and equip Ukraine's underfunded army with defensive equipment such as advanced radar.

Moscow denies all involvement in the conflict and has responded by banning the import of most Western food.

Biden used both his meeting Monday with Ukrainian President Petro Poroshenko and Tuesday's parliamentary appearance to drive home the message that Washington remained fully committed to Kiev despite the recent shift in global attention to Syria.

He said on Tuesday that Putin's repeated claims of big countries having the right to their own regional "spheres of influence" were out of step with modern times.

"Sovereign states have the right to make their own decisions and choose their own allies," he stressed.

Biden - viewed as US President Barack Obama's pointman on Ukraine - also used his visit to promote a more committed fight against the corruption that has ravaged the country of 40 million for years.

"It's not enough to set up an anti-corruption bureau and establish a special prosecutor in fighting corruption. Your office of the general prosecutor desperately needs reform" he said.

Russia's seizure of Crimea and the pro-Kremlin revolt came just weeks after public protests toppled former president Viktor Yanukovych - a Moscow-backed leader who led a lavish lifestyle and surrounded himself with tycoons suspected of graft.

Polls show that corruption remains one of Ukrainians' main concerns.

Biden also made an indirect reference to reported infighting between Poroshenko and Prime Minister Arseniy Yatsenyuk that has stalled the passage of vital economic and anti-graft laws.

"All of you must put aside your differences and make a real revolution of dignity," Biden said.

His address was met with three rounds of standing ovations by lawmakers of all political stripes.