Russia reduced gas supplies to Ukraine by an additional quarter on Tuesday after a 25 percent cut in a debt dispute, a spokesman for Russian gas monopoly Gazprom said on state television.
"Supplies of gas for Ukrainian consumers... have been reduced by an additional 25 percent," the spokesman, Sergei Kupriyanov, told reporters.
EU calls gas group meeting
The European Commission on Tuesday called a special meeting of its gas coordination group for next week, after Russia announced it was reducing supplies to Ukraine, a key transit nation for the EU.
The meeting "will ensure a fully coordinated EU response to the situation," the EU's executive arm said in a statement.
Earlier, a commission spokesman said that Russian gas giant Gazprom had assured Brussels there would be no cut in supplies to Europe despite a 50 percent reduction in its supply to Ukraine.
EU Energy Commissioner Andris Piebalgs and Andrej Vizjak, the economy minister for Slovenia, which holds the EU presidency, called for "a determined effort to resolve the current disagreement between Gazprom and Naftogaz Ukrainy".
The pair also insisted "that supplies to the EU remain uninterrupted," the commission statement said.
The EU's gas coordination group brings together energy experts from all 27 EU member states and European Commission representatives.
It helps coordinate European measures to safeguard the security of energy supplies and helps individual member states respond to any shortages or problems.
The group would probably invite a Russian and a Ukrainian representative to the meeting next Tuesday, commission spokeswoman Marilyn Carruthers told AFP.
To date, no EU member state has reported any reduction in supplies.
"The European Union considers that in the past Gazprom has demonstrated its commitment to be a reliable supplier of gas to the European Union, as has the Ukraine played a similar role as a transit partner of the EU," said Piebalgs.
"The EU ... looks to the parties to make every effort to find a rapid and durable solution to their disagreement. In addition, we look to both parties to ensure that gas supplies to the EU remain unaffected."
Gazprom insisted supplies to European Union customers via Ukraine would "be assured at full volume," but Ukraine's Naftogaz suggested it might divert gas transiting to Europe through Ukraine to make up for any shortfall.
The row echoes a 2006 dispute when Gazprom cut off all of Ukraine's gas exports because Kiev had refused to agree to a much higher price for supplies, triggering a ripple effect of shortages across Europe.
Russia supplies over 40 percent of the European Union's gas, much of which arrives via Ukraine.