Deliveries of Russian gas destined for Europe will not resume on Wednesday as hoped, according to the head of Ukraine's gas company, who blamed conditions set by Russia for the delay.

The news came as leaders from several European nations affected by the supply choke travelled to both countries to ask them to settle the issue. The European Union has warned of legal consequences for Russia and Ukraine for halting gas flows in mid-winter.

Russian gas company Gazprom turned on one natural gas tap to Ukraine, which carries most of the Russian gas destined for Europe in pipelines running through its territory, on Tuesday.

Ukrainian gas company Naftogaz did not deliver the gas to Europe, however, saying Gazprom had insisted it use a route that was technically arduous and would cut supplies to Ukrainian customers.

Naftogaz chief Oleh Dubina said Gazprom repeated its request again Wednesday, but that the Ukrainian gas company is refusing to block the flow to its own consumers.

Russia has selected a single gas entry point at its border and ordered the gas be transported to a pumping station near the Romania border, Ukrainian energy adviser Bohdan Sokolovsky said Tuesday, calling it a "technically impossible transit route."

The two points are not linked by an export pipeline and would require Ukraine to cut service to domestic consumers in its eastern industrial region before it can deliver gas to the Balkans, according to Sokolovsky.

Price dispute deadlock

Russia has not agreed to send natural gas to Ukraine for domestic consumption. The countries are deadlocked over the price for gas Ukraine will pay and the amount Russia should pay for transporting gas through the country.

Russia's gas cut-off has left large parts of Europe in the cold and dark in the mid-winter. Eleven people have reportedly frozen to death during the dispute.

Russian Prime Minister Vladimir Putin on Wednesday accused Ukraine of holding European nations hostage and insisted the EU should not accept Ukraine's claims.

"No matter what papers others provide, I'll burn them in the oven," he told the visitors, referring to Ukrainian documents sent to the European Union. "We opened the tap, and are ready to supply gas, but on the other side, the tap is closed."

Putin made the comments as he met with the prime ministers of Slovakia, Bulgaria and Moldova at his residence outside Moscow.

Slovakian Prime Minister Robert Fico said "Ukraine is losing the trust of European partners because of its behaviour."

"The most unpleasant part is that millions of Europeans feel like hostages and are truly suffering," said Bulgaria's Sergei Stanishev.

Ukrainian President Viktor Yushchenko travelled Wednesday to Poland for talks on the dispute.

Moscow alleges that Ukraine illegally siphoned off supplies meant for other European countries between Jan. 1 and Jan. 7 — a charge Kiev denies.

A deal signed Monday to restart the gas flow requires a EU-led monitoring mission at the metering and compressor stations across Ukraine.

The monitoring agreement is meant to allow European, Russian and Ukrainian experts to measure the flow of Russian gas through Ukrainian pipelines.

Jose Manuel Barroso, the European Commission's president, warned Gazprom and Naftogaz that he would advise European energy companies to sue them unless they make genuine efforts to restore gas supplies.

"If the agreement is not honoured, it means that Russia and Ukraine can no longer be considered reliable partners for the European Union in matters of energy supply," Barroso told the European Parliament.

Tens of thousands without heat

European Union officials said that when pumping resumes, it will take at least a day for gas to reach consumers in Europe, tens of thousands of whom have been left without heat as a result of the dispute.

Gazprom supplies one-quarter of all natural gas consumed by EU countries, and 80 per cent of that gas is piped through Ukraine.

Serbia's power grid was on the verge of an overload Wednesday as thousands switched to electric heat and residents were urged to conserve energy. Air pollution in Belgrade was also reportedly on the rise because of the shift from natural gas to oil.

Hungary issued its first-ever smog alert in Budapest last week for the same reason.

With files from the Associated Press