AT least 12 soldiers were killed today when a Ukrainian government military helicopter was shot down near Slovyansk.

Coup-installed acting president Oleksandr Turchynov told the Kiev parliament that pro-Russian rebels had used a portable air defence missile to bring down the chopper.

He said General Serhiy Kulchytskiy was among the dead.

Slovyansk, home to 120,000 people 100 miles from the Russian border, has become the epicentre of fighting between the Kiev government and its armed opponents in recent weeks.

Mr Turchynov said that the helicopter had been flying troops to a hill outside Slovyansk where Ukrainian forces have set up positions.

General Kulchytskiy once served in the Soviet Red Army and was in charge of combat training for Ukraine’s recently set up National Guards, drawing in many of the fascist street gangs central to February’s coup.

Slovyansk is in the Donetsk region, one of the two provinces in eastern Ukraine that have declared independence from the government in Kiev.

Its “people’s mayor” Vyacheslav Ponomaryov confirmed yesterday that his fighters were holding four missing Organisation for Security and Co-operation in Europe observers and promised they would be released shortly. 

Mr Ponomaryov added that the monitors, who are from Turkey, Switzerland, Estonia and Denmark, were safe.

“I addressed the OSCE mission to warn them that their people should not travel in areas under our control over the coming week. And they decided to show up anyway,” said Mr Ponomaryov.

“We will deal with this and then release them,” he said, without setting a specific timeframe.

OSCE teams have been deployed to Ukraine to monitor the security situation following Russia’s annexation of Crimea and the rise of the pro-Russia separatist insurgency in eastern Ukraine. 

They also observed Sunday’s presidential vote, won by billionaire confectionery magnate Petro Poroshenko.

Mr Poroshenko has promised to negotiate with people in the east but also vowed to uproot the armed rebels.

Russian President Vladimir Putin has supported an OSCE peace plan that calls for ending hostilities and launching a political dialogue and has said that Moscow would work with Mr Poroshenko.

His Foreign Minister Sergey Lavrov called for urgent international mediation yesterday to persuade Kiev to halt its “punitive operation” in eastern Ukraine.