European Commission President Jose Manuel Barroso said Russian Prime Minister Vladimir Putin and Ukraine President Yuliya Tymoshenko had agreed in principle to allow independent parties to monitor the pipeline shut down in a dispute over Ukraine's gas bill.

Russia and Ukraine have blamed each other for halting gas flows through the pipeline that delivers 80 percent of Russia's natural gas to Europe, The Times of London reported.

Several European countries have declared states of emergency as below zero temperatures gripped parts of the continent.

Bosnian Foreign Minister Sven Alkalay said "4 million of our citizens are in danger."

Austria, Bulgaria, Slovakia, the Czech Republic, Bosnia, Croatia, Greece, Hungary, Macedonia, Romania, Serbia and Turkey. France, Italy, Germany and Poland have reported supply disruptions.

Russia's energy giant Gazprom claims Ukraine owes $614 million in late fees for gas deliveries. Negotiations for Ukraine's 2009 contract have also broken down.

Russia also says Ukraine siphoned gas intended for Europe from the line.

Barroso said the two countries were holding Europe "hostage" to the situation.