Ukraine civil war: Pro-Russian rebels down army helicopter, killing 12 troops

Kiev: Ukraine's vow to crush the bloody insurgency in the industrial east of the country suffered a major blow Thursday when pro-Russian rebels downed an army helicopter, killing 12 soldiers including a general.

The militants shot the Mi-8 helicopter gunship out of the sky with a sophisticated surface-to-air missile, which the White House said raised concerns about the rebels being supplied "from the outside".

One of the separatists' leaders made a surprise admission Thursday that 33 out of more than 40 rebels killed during a raid on a Donetsk airport this week were Russian nationals from Muslim regions such as Chechnya.

The revelation challenged President Vladimir Putin's rejection of Russian links to the separatist drive and supports Kiev's claims that the rebels do not represent the true will of the miners and steel workers who have turned the east into the economic engine of Ukraine.

Moscow meanwhile called on Kiev to impose an immediate ceasefire and urged the West to use its influence to prevent "a national disaster" in Ukraine.

"The international community awaits from Kiev an immediate ceasing of military activities in the east of the country and the withdrawal of troops. Without that, achieving peace in Ukraine is impossible," the foreign ministry said in a statement.

The country's Western-backed president-elect Petro Poroshenko, winner of 54.7 percent of Sunday's vote and due to be inaugurated on June 7 needs to avert another showdown with Russia that could see his economically teetering nation cut off from gas supplies by the start of next week.

But cash-strapped Ukraine appeared to avert the immediate threat of a gas cut-off when the European Union announced that a new round of talks had been urgently set up for Friday in Berlin.