Pro-Russia rebels shot down a Ukrainian military helicopter in Slavyansk with portable surface-to-air missiles on Thursday, killing 14 people including an army general, according to the acting president, Oleksandr Turchynov.

Sporadic fighting has continued in the city in the Donetsk region following a battle for the local airport at the weekend in which at least 50 rebels were killed.

The Kiev government has condemned the insurgency in east Ukraine as the work of "terrorists" bent on destroying the country and blames Russia for fomenting the unrest. Moscow denies the accusations, saying it has no influence over rebels, who insist they are only protecting the interests of eastern Ukraine's Russian-speaking population.

But a group of largely Russian fighters known as the Vostok (east) battalion which has emerged at the head of the resistance has sought to assert its authority over disparate rebel factions and instil discipline in the armed separatist movement.

The unit includes fighters from Chechnya, recently annexed Crimea, and other parts of Russia and Ukraine. The unit played a large role in the battle for Donetsk airport, said a battalion member known as Ram.

On Thursday armed and masked men from the Vostok battalion took control of the Donetsk regional administration building, the heart of the insurgency, where pro-Russia protesters declared the Donetsk People's Republic in April.

After a standoff, during which snipers appeared on a nearby apartment building roof, the Vostok group began to clear the building of various rebel groups. On their command, bulldozers began to remove barricades of tyres, paving stones and barbed wire.

One of the Vostok battalion commanders, who identified himself as Ros, said the barricades were no longer necessary and posed a fire hazard. He said the building would be cleared so that officials of the Donetsk People's Republic could continue their protest.

"Why are there so many groups? We are one country," he said, referring to the declared republic.

Roman Romanenko, a former paratrooper and coalminer appointed to head the defence of the building in April, agreed there was a struggle between the Vostok battalion and the Donbass People's Militia.

Klavdia Kulbatskaya, a spokeswoman for the People's Republic, said the Vostok battalion was checking rebels from the Donbass People's Militia who had been accused of looting.

Two rebels were shot this week in Slavyansk for "looting, armed robbery, kidnapping, leaving battle positions" at the command of Igor Strelkov, a Russian-born leader whom Kiev authorities accuse of being a Russian intelligence agent.

Ros said the Vostok battalion had let the looters go and that the people would "deal with them".

Mark Galeotti, an expert in Russian security services, at New York University, who studies the Russian security services, wrote on his blog this week that the appearance of the Vostok battalion, which has its roots in a Chechen unit that fought in the 2008 Georgia war, was a move by Moscow to "reverse the slide towards warlordism" in eastern Ukraine and exert more control over the uprising it has encouraged.

The deaths of residents in the conflict has further inflamed hatred toward the Kiev government, which many already view with deep mistrust. Vladimir Putin has indicated that Moscow is ready to negotiate with the president-elect, Petro Poroshenko, and the new Kiev leadership. On Thursday, outside the Donetsk administration building, Rostislav, a telecommunications employee, whose company closed last month, said his friend "took up a machine gun" with the rebels after a shell hit his home during the heavy fighting in Donetsk on Monday.

One man outside the Donetsk morgue said: "If the Ukrainian military's aggression continues many people will join the rebellion. If my friends fighting with the rebels are hurt, or if my home is damaged, I won't run away, I'll take up weapons and join."