Joe Biden: "Ukraine faces a struggle for its very future". Photo: BBC NEWS

He was speaking during a joint news conference in Kiev with interim Prime Minister Arseniy Yatsenyuk.

Mr Biden warned Russia that further "provocative behaviour" would lead to "greater isolation" and urged Moscow to end its alleged support for pro-Russian militants in eastern Ukraine.

Meanwhile, the funerals took place for three men shot on Sunday.

Funerals for those killed at a pro-Russian checkpoint near Sloviansk took place on Tuesday

They were killed during a raid on a checkpoint manned by pro-Russian separatists near the town of Sloviansk in eastern Ukraine.

The local separatists said the attack was carried out by ultra-nationalist Right Sector militants but Kiev called it a "provocation" staged by Russian special forces.

The bodies of those killed lay in open coffins at the funeral ceremony at the Church of the Holy Spirit in the centre of Sloviansk.

'Endemic' corruption

Earlier in remarks to Ukrainian MPs, Mr Biden said the US stood with Ukraine's new leaders against "humiliating threats" - an apparent reference to Russia.

The vice-president called on Moscow to urge the pro-Russian separatists to leave the buildings they are occupying in eastern Ukraine, and to abandon checkpoints.

Mr Biden said Ukraine also stressed the need for the new authorities to tackle corruption, which he described as "endemic in your system".

He told members of parliament: "The opportunity to generate a united Ukraine, getting it right is within your grasp."

The US is to provide an additional $50m to help Ukraine's government with political and economic reforms.

This includes $11m to help run the presidential election due on 25 May. An additional $8m is being provided for non-lethal military assistance.

 

 

The BBC's Natalia Antelava visited a protest camp in Luhansk

Flowers lie on the road near the site of Sunday's fatal shooting

Pro-Russian militants are still holding official buildings in at least nine towns and cities in the Donetsk region

'Tatars banned'

Russian President Vladimir Putin on Monday signed a decree to rehabilitate Crimea's Muslim Tatars and other ethnic minorities who suffered during the rule of Soviet dictator Josef Stalin.

After a referendum in Crimea last month, the territory was incorporated into Russia, something Mr Biden said the US would never recognise.

Crimea's Tatar community opposed the peninsula's takeover by Russia. On Tuesday, the Tatar assembly said the leader of the community, Mustafa Dzhemilev, had been banned from returning to Crimea for five years, along with his deputy.

'Men in masks'

Moscow and Washington are accusing each other of breaking last week's Geneva accord on resolving the Ukraine crisis, and the US is planning further sanctions should Russia fail to fulfil its Geneva commitments.

But Russian Prime Minister Dmitry Medvedev told the Russian parliament on Tuesday that Russia would be able to "minimise the consequences" of any further sanctions.

The 17 April Geneva accord stipulated an immediate end to violence in eastern Ukraine and called on illegal armed groups to surrender their weapons and leave official buildings.

 

 

Sergei Lavrov: "All signs show that Kiev can't, and maybe doesn't want to, control the extremists who continue to call the shots"

Pro-Russian militants are still holding official buildings in at least nine towns and cities in the Donetsk region.

In Kramatorsk, a further official building - a police station - was seized on Tuesday.

Mr Biden again accused Russia of supporting "men in masks in unmarked uniforms" who the US says are directing pro-Russian activity in the East.

Moscow denies being behind the protests and seizures of buildings.

Ukraine says photos released by the Ukrainian government anddistributed by the US State Department show Russian soldiers among militants holding official buildings in eastern Ukraine.

Photos released by the Ukrainian government purport to show a soldier, circled in red, in both Kramatorsk and Sloviansk, and in a photo (centre) showing a group in the Russian Special Forces

There was no immediate response to the pictures from the Russian government.

Ukraine has been in turmoil since last November, when Kiev was gripped by protests over whether the country should lean more towards Russia or Europe.