MOSCOW (AP) — Russia’s state natural gas monopoly Gazprom says it’s beginning efforts to end its contract to supply gas to Ukraine, raising concerns about downstream gas supply to European countries.

Much of Russia’s gas to Europe is shipped via Ukraine’s pipeline system. A Russia-Ukraine gas dispute in 2009 significantly cut supplies to Europe in frigid winter weather.

Gazprom deputy chairman Alexander Medvedev said Saturday that the company has begun procedures in the Stockholm international arbitration court to end its contracts with Ukraine’s Naftogaz. The move comes after the Stockholm body ruled that Gazprom should pay Ukraine more than $2 billion for failure to deliver the agreed-upon volumes of so-called “transit gas.”

Naftogaz said in a statement Saturday that transit of gas to Europe “remains intact.”