Ukrainian leader vows to punish pro-Russia rebels

Militants shot down Mi-8 helicopter with surface-to-air missile, killing 12

Ukraine's president-elect Petro Poroshenko vowed to punish pro-Russian rebels who downed an army helicopter in the east of the country, killing 12 troops in one of the deadliest attacks of the insurgency.

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