Men wearing the uniforms of Ukraine’s now-defunct riot police occupied police headquarters in Donetsk, the eastern city that is one of the flashpoints of a wave of pro-Russia protests.
The occupation came hours after armed men seized local police headquarters and a local branch of the Security Service in a nearby city.
Interior minister Arsen Avakov described the unrest as “Russian aggression” and said Ukraine’s security chiefs were holding an extraordinary meeting.
In a phone call with Russian foreign minister Sergey Lavrov, US secretary of state John Kerry “expressed strong concern” that the attacks “were orchestrated and synchronised, similar to previous attacks in eastern Ukraine and Crimea”.
Mr Kerry “made clear that if Russia did not take steps to de-escalate in eastern Ukraine and move its troops back from Ukraine’s border, there would be additional consequences”, the State Department said.
The Russian news agency Itar-Tass, citing Russia’s Foreign Ministry, said Mr Kerry “could not give any concrete facts” to support his allegations. The news agency said Mr Lavrov told Mr Kerry that the crisis in Ukraine was due to the failure of the Ukrainian government “to take into account the legitimate needs and interests of the Russian and Russian-speaking population”.
The unrest in Donetsk and the city of Slovyansk, about 55 miles to the north, were the latest shows of spiralling anger in eastern Ukraine, which has a large Russian-speaking population and was also the support base for Viktor Yanukovych, the Ukrainian president who was ousted in February after months of protests in the capital Kiev.
Ethnic Russians in Ukraine’s east fear that the authorities who took over after Mr Yanukovych’s fall will suppress them.
In Slovyansk, the mayor said the men who seized the police station were demanding a referendum on autonomy and possible annexation by Russia. Protesters in other eastern cities have made similar demands after a referendum in Crimea last month in which voters opted to split from Ukraine, leading to annexation by Russia.
Witnesses said the men who entered the police building in Donetsk were wearing the uniforms of the Berkut, the feared riot police squad that was disbanded in February.
Berkut officers’ violent dispersal of a demonstration in Kiev in November set off vast protests in the capital that culminated in bloodshed in February when more than 100 people died in sniper fire; the acting government says the snipers were police.
It was not immediately clear if the men who occupied the Donetsk police building had made any demands, but the Donetsk police chief said he was forced to offer his resignation. Interfax Ukraine said pro-Russian protesters had invited the former police chief to resume his duties.
In Slovyansk, about 20 men in balaclavas and armed with automatic rifles and pistols were guarding the entrance to the police station in the city of about 120,000 people and another 20 were believed to be inside.
They wore St George’s ribbons, which have become a symbol of pro-Russian protesters in eastern Ukraine. The ribbons were originally associated with the Soviet Union’s victory in the Second World War.
A masked guard in Slovyansk, who gave his name only as Sergei, said they had “only one demand: a referendum and joining Russia.”
The man said they seized the building because they wanted to protect it from radical nationalists from western Ukraine and “the junta who seized power in Kiev”.
“We don’t want to be slaves of America and the West,” he said at the seized police station. “We want to live with Russia.”
Mr Avakov said in a Facebook post that unknown men opened fire on a police station in Kramatorsk, a town near Slovyansk, and police were engaged in a gunfight with them. In Krasnyi Lyman, another town in the area, men armed with Russian-made automatic rifles attacked a police station, he said.
The Interior Ministry said the attackers in Slovyansk used tear gas and stun grenades when they stormed the building, injuring three policemen. The attackers’ goal was to seize arms from the police station, authorities said, adding that there were about 40 automatic rifles and 400 pistols as well as ammunition inside.
The Interior Ministry said later that men from the same group seized the local Security Service building.
The Kiev authorities and the United States have accused Russia of fomenting the unrest in the east and seeking to use it as a pretext for sending in troops. Russia has reportedly massed forces in areas near the Ukrainian border.
But Slovyansk mayor Nelya Shtepa said she held talks with the protesters and they were locals and not Russians.
“They told me: ‘We don’t have anything against you,’ ” she said, adding that the men said they “want to be heard, want a dialogue with authorities in Kiev”.
US vice president Joe Biden will visit Ukraine on April 22. The US said the visit would focus on the international community’s efforts to help stabilise and strengthen Ukraine’s economy, as well as efforts aimed at constitutional reform, decentralisation, anti-corruption, and free and fair presidential elections set for May 25.