More than a week into the dispute, with international monitors in place to observe gas flows, Russia's state-run energy concern Gazprom accused Ukraine's Naftogaz of blocking deliveries intended for Europe, Deutsche Welle reported Wednesday.

Ukraine, in return, said Gazprom had deliberately engineered the delivery to make it impossible for Naftogaz to handle.

The prime ministers of Bulgaria and Slovakia scheduled visits to Moscow and Kiev, Ukraine, Deutsche Welle reported.

European Commission leader Jose Manuel Barroso informed Russian Prime Minister Vladimir Putin by phone of "EU's disappointment" that gas flows were still not reaching customers in Europe.

About 20 European countries have reported disruptions in gas deliveries.

Gazprom began cutting deliveries to Ukraine Jan 1, claiming Ukraine owed $614 million in late fees on its gas bill.