A "large explosion" cut the pipeline, which carries Siberian gas through Ukraine to Germany and other EU clients, said Viktoria Ruban, spokeswoman for the Ukrainian emergency situations ministry.

The blast occurred at about 1125 GMT close to the village of Luka on a section south of the Ukrainian capital Kiev, tearing out a 30-meter (32-yards) length of pipeline and hurling debris 150 meters (yards), she said.

"It's one of the most serious accidents in recent years," an official from the Ukrainian state gas company Naftogaz told AFP on condition of anonymity.

The official said the blast was likely due to a technical fault.

Emergency services put out a fire at the scene and investigators were working to uncover the cause of the explosion, Naftogaz said in a statement.

The incident immediately raised fears of gas shortfalls in Europe, which relies heavily on Russian supplies, but Russia's gas exporting monopoly Gazprom quickly assured that deliveries would still reach clients.

Assurances

"There will be no disruption in supplies to our consumers. Our export supplies will continue at full volume," Sergei Kupriyanov, a spokesman for Gazprom, said on state television.

Naftogaz also promised there would be no disruptions. "Ukraine's commitments on transit of natural gas to European customers are being completely respected," a company statement said.

The emergency situations ministry initially said that gas supplies had been cut following the blast but later added that a bypass route was used to ensure continued supplies.

In Poland, a spokesman for gas company PGNiG said the early signs were positive.

"There was no disruption to gas supplies," Tomasz Fill said. "It is difficult to foresee the consequences of the explosion for Poland. We are waiting for official information from Kiev."

The Urengoi-Uzhgorod pipeline has a capacity of 27.9 billion cubic meters (bcm) of gas a year, Interfax news agency reported -- a sizeable share of the 87.8 bcm exported to western Europe, according to 2002 figures from Gazprom.

The pipeline runs more than 4,000 kilometres (2,500 miles) from Siberia.

Biggest foreign market

The European Union is the biggest foreign gas market for Russia, the world's leading natural gas producer. Nearly all of Ukraine's energy imports come via Russia.

The incident revived memories of gas shortfalls throughout western Europe at the start of 2006 when Gazprom cut off supplies through Ukraine due to a pricing dispute with the ex-Soviet republic.

The 2006 crisis sparked concerns in the West over the reliability of Russia as a supplier and accusations that Moscow is using its huge energy reserves as a weapon against weaker ex-Soviet neighbors.