Officials confirmed that gas had reached Ukraine, Hungary, Slovakia and Bulgaria – some of the countries worst hit by the disruption to supplies.

The move comes after the Russian and Ukrainian prime ministers agreed a new contract on the price of gas.

Millions of Europeans have been without heat since the failure to renew the old contract, which expired on January 1st.

EU states import a quarter of their gas from Russia and 80% of supplies come via Ukraine. Almost 20 countries in Europe have been affected by the dispute, said the BBC.

Some countries, including Bulgaria and Slovakia, rely almost entirely on Russia for gas, pumped via Ukraine. Both nations have openly discussed reopening nuclear power reactors they had been required to shut down prior to joining the EU.

It is unclear if the countries intend to pursue the nuclear option with EU leadership.

EU Commission President Jose Manuel Barroso said the Europe could not allow a repeat of the gas stand-off.

"We have to stop simply talking about energy security in Europe, and start doing something about it," he said, according to the BBC.