Pro-Russian rebels shot down two Ukrainian helicopters yesterday, killing two crew, as troops tightened their siege of separatist-held Slavyansk and Moscow accused Kiev of launching a "criminal" assault that wrecked hopes of peace.
Though Ukrainian forces appeared to be carrying out one of their most concerted military operations yet, their advance on the ground was limited. Nevertheless, President Vladimir Putin's spokesman accused Kiev of firing on civilians from the air in a "punitive operation" that destroyed an international peace plan.
Russia was "extremely worried" about the fate of Russians in the city, including an envoy sent to help free German and other foreign hostages, the Kremlin spokesman said.
The dramatic language seems to raise the stakes, as Moscow has tens of thousands of troops massed on the border and claims the right to invade if needed to protect Russian speakers in the region.
In Slavyansk, the most heavily fortified bastion of pro-Russian separatists in eastern Ukraine, shooting broke out as one helicopter opened fire before dawn. Ten hours later, the city was largely quiet, with shops shut and armed separatists in control of the streets.
Advancing Ukrainian forces in armoured vehicles took up positions closer to the suburbs, but rebels still controlled most of the city of 130,000.
A day earlier the separatist pro-Russian militants had earlier more moves, seizing a rail control centre for the Donetsk region, a railway official said. By cutting off power, they had all but paralysed train traffic.
The Ukrainian Defence Ministry said that two Mi-24 attack helicopters had been shot down by shoulder-launched antiaircraft missiles while on patrol overnight around Slavyansk. Two airmen were killed and others wounded.
The aircraft normally have two crew but can carry more.
Other Ukrainian officials and the separatist leader in Slavyansk said earlier that one airman was taken prisoner.
A third helicopter, an Mi-8 transport aircraft, was also hit and a serviceman wounded, the Defence Ministry said. The SBU security service said this helicopter was carrying medics.
Nonetheless, Kremlin accounts of grave threats to civilians highlight the risk of a Russian move to seize territory ahead of a vote the rebels aim to hold on May 11 seeking a mandate to break with Kiev. The ballot is like one held in the Crimea region before Moscow annexed it.
Putin's spokesman, Dmitry Peskov, heaped blame on the Ukrainian government. Noting that Putin had warned before that any "punitive operation" would be a "criminal act", Peskov said this was what had now happened in Slavyansk.
The European Union said it was watching events in eastern Ukraine with growing concern.