Russia warns of gas risks to Europe after Ukraine fails to pay

An employee works on pipes made for the South Stream pipeline near a Gazprom logo at the OMK metal works in Vyksa in the Nizhny Novgorod region April 15, 2014. REUTERS/Sergei Karpukhin

MOSCOW/KIEV (Reuters) - Russia's Gazprom said on Tuesday there were serious risks to gas transit to Europe via Ukraine after Kiev failed to pay in advance for supplies as a dispute between the two countries intensified.

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