Dozens die in Ukraine clash

Russia has warned of "catastrophic consequences" after dozens of people were killed and scores injured in a deadly fire following a clash between pro-Ukrainian and pro-Russian protesters in a trade union building in the Black Sea port of Odessa.

The carnage came after a day of vicious street battles in which both sides hurled cobblestones and Molotov cocktails.

Ukrainian authorities said 31 people died in the blaze. Twenty-three of the victims died of carbon monoxide poisoning and eight died after leaping from upper-storey windows to escape the flames, the interior ministry said.

More than 50 people, including 10 policemen, have sought medical attention.

The street fighting, which has claimed other lives, opened a new front in a conflict that has split Ukraine .

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

Interior Minister Arsen Avakov said operations were continuing yesterday and that Ukrainian forces had taken a television tower in the town Kramatorsk, which lies south of Slaviansk.

"We are not stopping," he wrote on his Facebook page.

Russian-speaking eastern Ukraine has been the focus of concern in Western capitals since pro-Russian gunmen overran the region after Moscow annexed Ukraine's mainly Russian Crimea in March.

Clashes had also occurred in largely Russian-speaking Odes-sa, not far from Crimea, but no one had been killed there until this week.

The Kremlin said Kiev's military move against the insurgents "destroyed" the two-week-old Geneva agreement on cooling Ukraine's crisis.

Russian 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 "to protect Russian speakers".

Kiev said it was forced to act in eastern Ukraine because Moscow was backing groups there who were "putting civilians in danger, seizing hostages and creating an atmosphere of terror and violence".

The chaos is overshadowing a presidential election that the pro-Western leadership in Kiev is planning for May 25.

The rebels are planning a vote on May 11 to seek a mandate to break with Kiev, like one held in Crimea before Moscow took it over.

Moscow moved in on Crimea following the overthrow of Ukraine's pro-Moscow president by protesters angered by his decision to scrap a trade deal with Europe.

The US and Europe have imposed sanctions on individuals over the Ukraine crisis, but they have had limited impact.

US 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 this week, told a joint news conference with Obama that the elections on May 25 were critical and sectoral sanctions were ready.

The energy and banking sectors are likely targets.

Putin's popularity has soared with the seizure of Crimea and talk of restoring Moscow's former empire. This week, he restored the Soviet-era tradition of holding a May Day parade on Red Square, where marchers carried banners hailing the acquisition of Ukrainian territory.