KIEV, June 19 – Europe’s natural gas supplies will be at risk in the winter after Russia’s sudden decision to cancel an important contract with the Ukrainian gas shipper, Naftogaz Ukrayiny reported Thursday.

Gazprom of Russia indicated it will cancel the contract allowing Ukrtransgaz, the gas shipper, to quickly increase supplies to Europe when demand there suddenly accelerates.

The contact, signed in 2010, called for Ukraine to tap its underground gas storage facilities to boost supplies before Gazprom could physically deliver any extra gas to the European border.