Ukraine says Russia is not sending enough gas to ensure EU supplies
Ukraine has warned that there could be serious problems with gas supplies for European Union countries if its dispute with Russia is not settled soon.
An energy official in Kiev said technical problems could disrupt flow.
Several EU countries have reported a drop in gas deliveries, apparently as a result of the dispute.
Romania, Hungary, Poland and Bulgaria said the pressure in their pipelines fell after Russian gas giant Gazprom cut off Ukraine's supply.
Gazprom says it can no longer count on Ukraine as a transit route to EU countries and is seeking alternatives.
In a BBC interview, the deputy chairman of Gazprom, Alexander Medvedev, said he hoped EU countries would back the move.
The firm has since accused Ukraine of stealing gas.
The Czech Republic, which holds the rotating EU presidency, is to convene a meeting of envoys in Brussels on Monday to discuss the row.
Both Russian and Ukrainian officials are visiting European capitals to put their case.
Pressure 'to fall'
Ukrainian energy official Bohdan Sokolovsky said problems for the EU would start in 10 days if Moscow failed to increase the supply.
"If the Ukrainian pipeline does not receive the required gas volumes, the pressure in the pipes is going to fall," he said, quoted by AFP news agency.
"As result, there will be interruptions quite automatically, independent of people. The system could even have to shut down so that the pressure comes back."
On Friday, Ukraine's state gas company, Naftogaz, denied illegally siphoning Russian gas, saying it was diverting gas from its own reserves to try to maintain export supplies.
Russia meanwhile has said it increased the volume of gas bound for the EU as it cut supplies to Ukraine.
Consumers 'not hit'
The head of Romania's gas pipeline operator Transgaz said gas supplies had dropped by 30% on Friday.
The deputy chairman of Gazprom, Alexander Medvedev, speaks to the BBC
The head of Bulgaria's state gas concern told Reuters news agency Bulgaria's supply was also falling and that transit to Turkey, Greece and Macedonia was affected.
Officials in both countries said consumers had not so far been affected.
On Friday, Poland reportedly recorded a drop of 6%, and Hungary a drop of almost a quarter.
In his first foreign interview since the gas was cut off to Ukraine, Gazprom's Alexander Medvedev dismissed the suggestion his company was deliberately picking a fight with Kiev.
Instead he said Gazprom was ready to end the dispute immediately - but there was no-one to negotiate with.
Mr Medvedev said Gazprom had gone out of its way to ensure supplies of gas to Europe were maintained.
He said the problem was not with Russia, but Ukraine, adding "that's why we believe it's necessary to develop, as soon as possible, alternative transit routes".
The alternatives are two new pipelines Russia is planning to build that will by-pass Ukraine on their way to Western Europe.
The Nord Stream gas pipeline would run under the Baltic Sea from Russia to Germany, and the South Stream link would pass under the Black Sea.
The BBC's Rupert Wingfield-Hayes in Moscow says this latest dispute is expected to give those Russian plans a significant boost.
Pipes across Ukraine carry about a fifth of the EU's gas needs. A similar row between Gazprom and Ukraine at the beginning of 2006 led to gas shortages in several EU countries.