The move follows back-and-forth phone calls by EU head commissioner Jose Manuel Barroso to Russian Prime Minister Vladimir Putin and his Ukrainian counterpart Yulia Tymoshenko late Sunday, Jan. 11.

Russian President Dmitry Medvedev earlier Sunday had rescinded the EU-brokered accord, citing changes by Ukraine.

He said Russia objected to handwritten text added to the formal agreement by the Ukrainian side, calling it a "mockery of common sense."

The extra declaration, which was seen by Reuters, asserted that Ukraine had not siphoned off transit gas and that it had no outstanding debts to Gazprom. That is the issue that stands at the center of the dispute.

"I think that those who have signed this document with reservations well understand the legal consequences of their actions," he told Foreign Minister Sergei Lavrov in a televised discussion.

"As a result, we are obliged to consider the document signed as null and void for us. We will not apply it as long as this reserve is not overturned," he added.

Putin charged that the Ukrainian additions had distorted the meaning of the document originally signed by both parties and introduced issues that were unrelated to the gas dispute.

The Czech Republic's energy envoy, Vaclav Bartuska, whose country holds the EU's rotating presidency, said the additional conditions added by Ukraine would not have changed the legality of the mandate for the EU observer mission.

Russian refusal to restart supplies

Moscow had insisted it would not restart gas supplies to Europe until a valid deal was signed. Supplies have been halted since Wednesday, Jan 7.

Medvedev had urged EU officials to pressure Ukraine into withdrawing its so-called declaration that it issued to accompany the agreement.

The European Commission says the declaration would not have changed the deal, but Lavrov told Medvedev that the copy of the deal Russia had received contained Ukraine's stipulation that it was only valid along with the declaration.

Putin had proposed to European Commission President Jose Manuel Barroso that Russian and EU officials meet in Brussels on Monday for talks over the gas row, a Russian government source told Reuters.

Putin told Barroso over the phone that additions made by Ukraine to an agreement on the monitoring of gas transit were "unacceptable." The Russian leader proposed the Brussels meeting to seek a solution, the source said.