Pro-Russian militants raised their flags over official buildings in two eastern Ukrainian cities on Saturday, deepening a stand-off with Moscow which, Kiev warned, was dragging Europe closer to a "gas war" that could disrupt supplies across the continent.
At least 20 men armed with pistols and rifles took over the police station and a security services headquarters in Slaviansk, about 150 km (90 miles) from the border with Russia.
Officials said the men had seized hundreds of pistols from arsenals in the buildings. The militants replaced the Ukrainian flag on one of the buildings with the red, white and blue Russian flag. Some local residents helped the militants build barricades out of tyres in anticipation that police would try to force them out, a Reuters photographer at the scene said.
But it was not clear how the authorities would tackle the militants after the police chief for the region quit. Kostyantyn Pozhydayev came out to speak to pro-Russian protesters outside his offices in the regional capital, Donetsk, and told them he was stepping down "in accordance with your demands." Some of his officers left the building.
The protesters were occupying the ground floor of the Donetsk police headquarters and the black and orange flag adopted by pro-Russian separatists flew over the building, in place of the Ukrainian flag, a Reuters reporter said. The occupations are a potential flashpoint because if protesters are killed or hurt by Ukrainian forces, that could prompt the Kremlin to intervene to protect the local Russian-speaking population, a repeat of the scenario in Crimea. Moscow denies any plan to send in forces or split Ukraine, but the Western-leaning authorities in Kiev believe Russia is trying to create a pretext to interfere again. Nato says Russian armed forces are massing on Ukraine's eastern border, while Moscow says they are on normal manoeuvres.
Ukraine's acting foreign minister, Andrii Deshchytsia, said he had spoken in a phone call with Russian Foreign Minister Sergei Lavrov and demanded Moscow stop what he called "provocative actions" by its agents in eastern Ukraine. Russia and Ukraine have been in confrontation since protests in Kiev forced the Moscow-backed president from office, and the Kremlin sent troops into Crimea. While the crisis within Ukraine itself is still unresolved, the gas dispute threatens to spread the impact of the row to millions of people across Europe.
A large proportion of the natural gas which EU states buy from Russia is pumped via Ukrainian territory, so if Russia makes good on a threat to cut off Ukraine for non-payment of its bills, customers further west will have supplies disrupted. Russia is demanding Kiev pay a much higher price for its gas, and settle unpaid bills.