Ukraine crisis: Dozens die in fire in Odessa

At least 31 people were killed in Odessa when a building was set alight during clashes between pro-Kiev and pro-Moscow factions.

Several of the dead were reported to have been killed when they jumped to escape the blaze and the rest died as they were overcome by fumes, heat and flames.

Police put the death toll at the trade union building at 31 but did not say how the fire broke out. Earlier in the day they reported that three people had been shot dead and a further 15 were hurt during in violent street battles.

Until yesterday the port of Odessa, in the southern part of Ukraine, had been largely untroubled by violence since President Viktor Yanukovych fled to Russia.

However, the attempt by the Kiev government to wrest back control of the eastern city of Slovyansk from pro-Russian militias sparked clashes between government and pro-Russia supporters.

In the town, pro-Russian separatists brought down two Ukrainian military helicopters involved in an operation to try to dislodge militants from their strongholds.

President Vladimir Putin's spokesman said Ukrainian forces had fired on civilians from the air in Slaviansk in a “punitive operation” that destroyed an international peace plan. Moscow has tens of thousands of troops massed on the border and claims the right to invade if needed to protect Russian speakers.

But the Western-backed government in Kiev said the use of missiles to bring down its helicopters showed Russian forces were in the town, an accusation which Moscow denies.

Ukraine's acting president also said Russian “armed saboteurs” had tried to enter the country overnight, but were pushed back by Ukrainian border troops. Russia's Security Service said the report was untrue.

The growing chaos is overshadowing a presidential election the pro-Western leadership in Kiev is planning for 25 May. The rebels are planning a vote on 11 May to seek a mandate to break with Kiev, like one held in Crimea before Moscow took it over.

In an attempt to ease tensions in the area, the United States and Europe have imposed sanctions on individuals, with little impact.

U.S. President Barack Obama said the next step would be sanctions on sectors of the Russian economy and they would be imposed if Moscow impeded the Ukrainian presidential poll.

German Chancellor Angela Merkel, visiting Washington, told a joint news conference with Obama that the elections on May 25 were critical and sectoral sanctions were ready.

The clashes in Ukraine prompted the UK to accuse Moscow at an emergency meeting of the UN Security Council of “synthetic indignation” and “breathtaking” hypocrisy.

Sir Mark Lyall Grant, the UK ambassador to the UN in New York, said Russia "funded, equipped and directed" some of those involved in the insurgency.

"The scale of Russian hypocrisy is breathtaking. Russia stoutly supports and indeed arms the most repressive regimes in the world, notably Syria, a regime which brutally represses dissent without any sense of restraint or concern for the protection of civilians,” he told the Security Council.

"Russia's synthetic indignation of Ukraine's proportionate and measured actions convinces no one."

Sir Mark said it was "simply not credible" for Moscow to claim the pro-Russian forces in Ukraine were "peaceful activists" given the apparent use of man-portable air defence systems.

"The use of such sophisticated weaponry against Ukrainian forces reaffirms our assessment that the armed groups in east Ukraine include professionals funded, equipped and directed by Russia."

Gerard Araud, the French ambassador, added: "Russia ... has released bands of thugs on Ukraine ... and is suddenly discovering this mixture might escape its control."

With Russia able to veto any motion the Security Council meeting broke up without any agreement being reached.

Earlier in the day Foreign Secretary William Hague, who will visit Ukraine next week, had said: "I am extremely concerned by reports of the activities of armed pro-Russian separatists in eastern Ukraine, including the detention of hostages, intimidation of the media and the reported shooting down of Ukrainian military helicopters this morning.

"There can be no doubt that these incidents, perpetrated by well-trained groups using sophisticated military technology, are intended to provoke further instability. These provocations are destroying all efforts to reduce tensions and are a serious threat to the country.

"Ukraine has shown admirable restraint since the beginning of this crisis in the face of extreme provocation on its own national territory.

"Now more than ever it is important that all parties, including the Russian Federation, abide by the commitments they made in Geneva on 17 April. I urge the Russian authorities to act to reduce tensions and to call upon separatist groups to lay down their arms."

Additional reporting: Reuters