European Union officials on Monday played down the impact of the gas dispute between Ukraine and Russia despite supply disruptions that are making some countries in Europe dip into gas reserves.

The cutoff of Russian natural gas supplies to Ukraine on Jan. 1 has caused some irregularities, but there has been no substantial disruption of supply to any member state, said EU spokesman Ferran Tarradellas.

Ukraine has continued shipping Russian gas to Europe through its pipelines, but some EU countries have reported significant declines in supplies as pressure in the pipelines dropped. Europe relies on Russia for a quarter of its natural gas and most of it is transported through pipelines that cross Ukraine.

Hungary, Romania and Bulgaria said Monday that supplies remained down, in Romania's case by 30 percent. Poland and the Czech Republic also have reported shortfalls in gas deliveries.

Some of these countries have been able to compensate for the supply drops by dipping into their reserves or through increased supplies from other sources.

We are confident there is going to be no problem of supply in the coming weeks for end consumers in Europe, Tarradellas said.

An EU mission was to arrive Monday in Kiev. After meeting with Ukrainian energy and other officials, the mission was to meet later in the week with officials of Russia's state-controlled gas giant Gazprom.

During a similar dispute between Ukraine and Russia in 2006, several West European countries saw their gas supplies drop by 30 percent or more. This time Gazprom's customers were better prepared, having built up substantial reserves. Gazprom also has taken additional steps to guarantee supplies.

While the previous gas cutoff was seen as punishment for Ukraine's pro-Western policies, this time Gazprom is insisting it is a commercial dispute. Both countries are seeking to prove they are a reliable energy partner for the EU.

Ukraine and Russia blame each other for the shortfalls. Gazprom accused Ukraine of stealing about 8 percent of the gas that it has pumped. Ukraine's state gas company Naftogaz says that Gazprom is refusing to send the extra so-called technical gas used as fuel to make the delivery, so it is using the missing gas for this purpose.

Ukraine has enough supplies to last for weeks. But it says that a continuing cutoff will lead to major delivery disruptions in Europe in less than two weeks. Ukrainian officials say that a continuing drop in pressure in the transport system will trigger an automatic shutdown until a minimum of gas accumulates, leading to temporary disruptions in supplies.

Both countries are accusing each other of resorting to blackmail and of an unwillingness to compromise.

Gazprom cut off supplies after negotiations broke down Wednesday over a contract for 2009 and outstanding debt. There have been no face-to-face negotiations since then.

Gazprom toughened its negotiating stance Sunday, saying it wants to charge Ukraine as much as $450 per 1,000 cubic meters in January, up from its offer before the cutoff of $250, which Kiev turned down. Kiev says that any price hike should be accompanied by a similar increase in the transit fee that Ukraine charges.

The Ukrainian president's energy adviser Bohdan Sokolovsky dismissed the offer of $450 as unacceptable.

It once again proves that the Russian side has no economic calculations about how the price should be formed, he said in a telephone interview, adding that Moscow was applying political pressure.

Ukraine attempted to crank up pressure on Russia on Monday, saying that Naftogaz may be prohibited from transporting Russian gas at a low transit fee.

Kiev's Economic Court has ruled to temporarily invalidate a transit contract with Russia on the grounds that the official who signed it in 2006 was not authorized to do so, said Naftogaz spokesman Valentyn Zemlyansky. Court officials were unavailable for comment due to public holidays.

The contract, valid through 2010, sets the transit fee at $1.60 per 1,000 cubic meters for 100 kilometers of transit. This means that the contract from 2006 may be proclaimed invalid, Zemlyansky said.

However, Ukraine is already charging Russia $1.70, based on an addendum to that contract. The lawsuit, filed by Ukraine's Fuel and Energy Ministry, appeared aimed at putting pressure on Russia.