Russian PM Vladimir Putin welcomes Slovakia's PM Robert Fico (L), Bulgarian PM Sergei Stanishev (2nd L) and Moldova's Zinaida Greceani at Novo Ogaryovo residence outside Moscow, 14 Jan 2009

The leaders of Bulgaria and Slovakia headed to Russia and Ukraine Wednesday to coax both countries to restart gas shipments to Europe a day after promises to do so were not honored. The gas crisis that has left many European countries in the cold.

The two European prime ministers are holding talks with their Russian and Ukrainian counterparts Wednesday in hopes that shipments of Russian gas via Ukraine will be resumed. Both Moscow and Kyiv agreed to resume natural gas supplies on Tuesday under a European Union brokered agreement. Gas began flowing - but only for several hours.

European Commission President Jose Barroso told the European Parliament Wednesday that it was "unacceptable and incredible" that gas flow has not resumed  and he said it means Russia and Ukraine can no longer be considered as reliable supply sources. He called on european companies to take legal action if gas did not start flowing.

A disappointed Jacek Saryusz-Wolski, who chairs the Foreign Affairs Committee for the European Parliament, told reporters in Brussels that gas shipments appeared to have stopped - with EU monitors in place at points along the supply route to confirm this.

"We got information that the gas no longer flows. The gas has stopped flowing. So we are again at the beginning and we cannot concentrate on sustainable long-term solutions - which we will anyway one day have to devise and agree upon - but left again to this crisis which does not seem to be ending," said Saryusz-Wolski.

Russian gas bound for Europe stopped flowing last week, affecting local gas supplies of about 20 European countries. Balkan nations were among those hardest hit, with thousands of households without heat. Schools, hospitals and factories have been forced to close.

Russia and Ukraine have traded accusations on who is responsible for the gas cutoff, with Russian gas giant Gazprom accusing Ukraine on Tuesday of blocking the gas. Ukraine in turn blamed Russia for routing shipments in a way it was unable to pump the gas on to Europe.

About a quarter of EU gas comes from Russia. The 27-member bloc is looking at ways to diversify its energy supplies - notably by tapping more into renewable sources - along with changing routes and sources. But it will take time before it can become less reliant on Russian gas.