Speaking at the European Parliament, Barroso also said that unless gas started flowing soon he would advise the bloc's 27 member states to take measures to secure alternative long-term suppliers of energy.

"I would like to convey a very clear message to Moscow and Kiev. If the agreement sponsored by the EU is not honoured as a matter of urgency, the Commission will advise EU companies to take this matter to the courts," he said.

"The current situation is in short most unacceptable and incredible," Barroso said during a debate on the EU's programme for the first half of this year.

"If the agreement is not honoured, it means that Russia and Ukraine can no longer be regarded as reliable."

Czech Prime Minister Mirek Topolanek, who holds the EU's rotating presidency for the first half of this year, told the debate that gas agreements must be made more transparent to avoid energy cuts in the future.

He added that as part of bolstering its energy security the EU should step up efforts to build the Nabucco pipeline, which might one day carry Caspian or Middle Eastern gas to the EU.

EU countries should also increase minimum crude oil storage to 120 days from the current 90 days, he said

Meanwhile, it emerged that Naftogaz today declined a request by Gazprom to supply almost 100 million cubic metres to the Balkans and Moldova, instead proposing alternative routes.

Naftogaz, in a note sent to Gazprom and seen by Reuters, said Ukraine had proposed directing gas to the Pisarevka and Valuiki compressor stations, rather than the Sudzha station proposed by Gazprom.

Russia began pumping gas meant for Europe via Ukraine on Tuesday, but the EU said little or no gas was flowing to countries suffering urgent energy shortages.

Russia accused Ukraine of shutting off gas to Europe, but Kiev said there was not enough pressure in the pipeline system.

Ukraine's energy ministry has asked the European Commission to help it secure from Russia "technical gas" needed to transit supplies to Europe.

"We clearly stated in our letter which technological sectors must be opened up today in order for Ukraine to oversee transit of gas to European countries," Energy Minister Yuri Prodan said in a statement.

"We asked the European Commissioner for his help for the technical gas, without which it is impossible to ensure transit."

The crisis has disrupted supplies to 18 countries.

Bulgaria and Slovakia, both EU member states and among the worst-hit by the crisis, today launched a round of fresh diplomacy to end the dispute that has left them without Russian gas for one week.

Both Sofia and Ljubliana sent their prime ministers to Moscow and Kiev in a fresh effort to get gas supplies restored.

Slovakian Prime Minister Robert Fico, who was in Kiev today for talks with Ukrainian Prime Minister Yulia Tymoshenko, said the country had 11 days of gas reserves left.

"After 12 days, we will be obliged to resort to measures never seen in our history. May I simply ask how long this will go on?" he told Tymoshenko.

But Tymoshenko said her country could do little to help. "Ukraine does not have sufficient gas. We do not have our own supplies," she told Fico.

Fico is meeting Russian Prime Minister Vladimir Putin alongside Bulgarian Prime Minister Sergei Stanishev and Moldovan Prime Minister Zinaida Greceanii today.

Stanishev is under pressure to secure supplies for his country of 7.6 million people as limited domestic reserves are dwindling and anger among Bulgarians is mounting against his Socialist-led government.

At the start of the meeting, Putin said European officials could do more to influence Ukraine.

"In my view, European officials could do more to put pressure on the transit country to ensure European interests," he said.

A deal brokered by the EU, which gets a quarter of its gas from Russia, had been intended to get supplies moving on Tuesday, with international monitors in place to ensure that Ukraine was not siphoning off any gas, as Moscow has alleged.

Gazprom declared force majeure on gas exports to Europe last night, with Russian President Dmitry Medvedev, a former top Gazprom executive, saying the company lost $1.1 billion so far due to lower gas exports to Europe caused by the dispute. On Sunday, Putin said Gazprom had lost $800 million.

Gazprom is demanding Kiev hand over $614 million for unpaid gas bills and pay $450 per 1000 cubic metres of gas this year. That is similar to rates paid by EU customers but a big rise on last year's price of $179.5 per Mcm.

Analysts in Kiev said Ukraine, saddled with debt and hard hit by the global slowdown, cannot afford that price.

The row, which has dented the reputation of both Moscow and Kiev as energy suppliers, also reflects their poor political relations. Moscow is vehemently opposed to moves by Ukraine's pro-Western leadership to join the US-led Nato alliance.

Meanwhile, Ukrainian Prime Minister Yulia Tymoshenko said she wanted talks on gas with Russia to be conducted at government level rather than between the two countries' gas companies.

Tymoshenko said government officials had been in contact with Putin's office to arrange a telephone conversation between the two premiers.

"Today, our goverment's protocol department has spoken to the Russian government's protocol department to discuss today how to make talks between Gazprom and Naftogaz the direct work of the two governments," she told a news conference.

Published: 14 January 2009 09:05 GMT  | Last updated: 14 January 2009 13:29 GMT