Ukraine's Naftogaz says Russia failed to deliver prepaid gas

KIEV (Reuters) - Ukrainian state energy firm Naftogaz accused Russia's Gazprom on Monday of failing to supply gas that Kiev had paid for in advance, days after Moscow said it was sending some supplies for Ukraine directly to regions held by rebels.

A dispute over Russian gas supplies and pricing for Ukraine has played out behind the scenes throughout the past year while Ukrainian forces have battled pro-Russian separatists in a war that has killed more than 5,600.