Slovakia is one of the countries worst-hit by the crisis
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Russia and Ukraine have invited the European Union to see for itself which country is to blame for the cut in supplies that has prompted Slovakia to declare a state of emergency and Bulgaria a crisis.
Ukraine wants EU monitors to confirm that Russia's energy company Gazprom is sending no gas down the pipeline.
Moscow says it has been, but is now cutting supplies.
It says Ukraine was stealing gas meant for other European countries.
Much of Europe gets its gas from Russia through Ukraine and they are being affected by the dispute.
Bulgaria, the Baltics, Slovakia and Hungary are almost 100% dependent on Russia for gas and some places have had no gas for more than 24 hours.
Romania, Bosnia-Hercegovina, Croatia, Greece, Macedonia, Serbia, and Austria have also had their supplies reduced.
Listen at the BBC World Service:
http://www.bbc.co.uk/worldservice/news/2009/01/090107_gas_russia_sl.shtml_______________________
Dependence on Russia for gas:
100% dependent on Russia: Latvia, Slovakia, Finland, Estonia
More than 80% dependent: Bulgaria, Lithuania, Czech Republic
More than 60% dependent: Greece, Austria, Hungary
http://news.bbc.co.uk/2/hi/europe/7814743.stm#map________________________