This article is more than 6 years old

This article is more than 6 years old

More than 30 people were killed in violent and chaotic clashes in the southern Ukrainian city of Odessa on Friday as pro-Ukraine activists stormed a building defended by protesters opposed to the current government in Kiev and in favour of closer ties with Russia.

The violence continued on Saturday as Ukraine said its forces had attacked pro-Russian separatists in the industrial east of the country at dawn near the town of Kramatorsk.

Interior minister Arsen Avakov said Ukrainian forces had seized control of a television tower in Kramatorsk, near the rebel stronghold of Slavyansk where there was heavy fighting on Friday. "We are not stopping," Avakov wrote on his Facebook page, but gave no information on casualties.

Odessa's large Soviet-era trade union building was set alight on Friday as the pro-Ukraine activists mounted an assault as dusk fell. Police said at least 31 people choked to death on smoke or were killed when jumping out of windows after the trade union building was set on fire.

Bodies lay in pools of blood outside the main entrance as explosions from improvised grenades and molotov cocktails filled the air. Black smoke from the building and a burning pro-Russia protest camp wreathed the nearby square.

Pro-Russia fighters mounted a last-ditch defence of the burning building, throwing masonry and petrol bombs from the roof on to the crowd below.

A pro-Russia activist aims a pistol at supporters of the Kiev government during clashes in the streets of Odessa. Photograph: Sergey Gumenyuk/Reuters

Medics at the scene said the pro-Russia fighters were also shooting from the roof. At least five bodies with bullet wounds lay on the ground covered by Ukraine flags as fire engines and ambulances arrived at the scene.

Some people fell from the burning building as they hung on to windowsills in an attempt to avoid the fire that had taken hold inside. Pro-Ukraine protesters made desperate efforts to reach people with ropes and improvised scaffolding.

"At first we broke through the side, and then we came through the main entrance," said one pro-Ukrainian fighter, 20, who said he was a member of the extreme nationalist group Right Sector.

"They had guns and they were shooting … Some people jumped from the roof, they died obviously," he said.

Riot police arrived on the scene as hand-to-hand fighting was already under way inside, but did not enter the building and stood formed up in ranks outside.

A protester walks past a burning pro-Russia tent camp near the trade union building in Odessa. Photograph: Yevgeny Volokin/Reuters

Within two hours of the assault beginning, the resistance from pro-Russia activists inside the building seemed to have been quelled. Several fire crews were spraying the smouldering building with water and ambulances lined the streets outside.

Bloody and dazed pro-Russia protesters were eventually escorted from the building. Many were handed over to police, and loaded on to police vans. Some were assaulted by the crowd.

"The aim is to completely clear Odessa [of pro-Russians]," said Dmitry Rogovsky, another activist from Right Sector whose hand had been injured during the fighting. "They are all paid Russian separatists."

The seizure of the trade union building was the violent culmination of a day of street battles in this Black Sea resort city.

The clashes reportedly began after protesters gathering for a rally in support of a unified Ukraine were attacked by pro-Russia activists armed with clubs and air pistols.

But the confrontation quickly escalated into a series of skirmishes as the two sides played a deadly cat and mouse game in the centre of the city.

Police largely stood aside as the two sides hurled molotov cocktails, cobblestones and bricks at each other. Girls as young as fourteen were smashing cobblestones to break them up into missiles of a manageable size.

Combatants on both sides were armed with body armour, helmets and shields and carried baseball bats, chains, metal bars and air pistols.

For two and a half hours the police were absent, said Olga Gold, a teacher watching the unrest. "The authorities have been absolutely indifferent," she said.

Dozens of buildings and cars were damaged during the violence. Most of the cafes and bars in central Odessa, a popular holiday spot, were closed by early evening.

A wounded man is treated after clashes in Odessa. Photograph: Sergey Gumenyuk/EPA

Meanwhile in the east of the country on Friday Ukrainian military forces mounted their fiercest attempt yet to retake Slavyansk – the town at the centre of the pro-Russia insurrection – obliterating checkpoints and losing two helicopters in an assault that has tilted the country closer to outright conflict.

At least two Ukrainian crewmen died when the Mi-24 helicopters were brought down by sophisticated missiles, and Stella Khorosheva, a spokeswoman for the insurgents, said three fighters and two civilians were killed in the clashes.

The claims could not be verified but the escalation resulted in the deadliest day in Ukraine since a dozen towns and cities fell to pro-Russia gunmen last month.

On Friday night, Slavyansk was calm but tense as pro-Russia gunmen regrouped in the rain.

Moscow responded by calling for a special UN security council meeting, saying the deal agreed in Geneva two weeks ago to defuse the situation had been buried by the Ukrainian onslaught. "The Kiev regime moved combat air forces against peaceful settlements, began a reprisal raid, essentially finishing off the last hope for the feasibility of the Geneva accords," said Dmitry Peskov, spokesman for Vladimir Putin. But there were no indications of an imminent Russian invasion. Instead, Moscow sent an envoy to try to help release foreign military observers who have been held hostage in the city.

The sudden escalation dominated exchanges between Barack Obama and Angela Merkel in Washington. The US and Europe have sought to coordinate their response to the crisis, imposing two rounds of sanctions aimed at Putin's inner circle and freezing assets of companies linked to them. On Friday they warned Russia that sanctions targeting whole sections of the country's economy would be inevitable unless Moscow de-escalates the situation in Ukraine before elections later this month.

Barack Obama and Angela Merkel hold a joint news conference in the Rose Garden. Photograph: Alex Wong/Getty

"Putin's views must be taken into account in Ukraine, but Russia does not have the right to violate Ukrainian territorial integrity or dictate Ukrainian domestic policy," Obama said.

Merkel also gave a strong endorsement of potential new sanctions. "In Europe, we have taken a position that should further destabilisation happen, we will move to a third stage of sanctions," she said.