BRUSSELS (AP) — European Commission President Jose Manuel Barroso warned EU countries Friday to prepare for another natural gas supply crisis if Ukraine can't pay for gas imports from Russia.

Russia sends the gas it sells Europe through pipelines that cross Ukraine and has cut off all supplies — including gas intended to heat European homes and fuel power plants — in previous disputes with Kiev.

Moscow recently warned it could shut off supplies again if Kiev does not pay on time and in full. Ukraine has called for $4 billion in loans from international banks to pay the bill.

Barroso announced plans to host urgent talks next week at EU headquarters with gas companies, the International Monetary Fund and member states "to look at whether a short package of stop gap funding can be put together."

"We have also advised vulnerable member states to take immediate measures to respond to a possible crisis," Barroso said. "We should also be ready for the worst."

Europeans complain they are hostage to disputes between Russia and its neighbors, warning that this forces them to seek other sources and routes for the energy it imports. Millions of people went without gas during a January dispute between Russia and Ukraine.

"We must not sleepwalk into another gas crisis," Barroso said. "There is indeed the risk of another major crisis in weeks, not months and we must protect European citizens."

Ukraine's Prime Minister Yulia Tymoshenko has already been in talks with the European Bank for Reconstruction and Development about the loan but will also hold talks with other financial institutions.

Ukraine must pump some 30 billion cubic meters of gas into its underground storage facilities over spring and summer months to be used during the winter heating season, according to the state company Naftogaz. The company says it has 16 billion cubic meters of gas left to pump this year in addition to monthly gas purchases used mostly for industrial needs.

Tymoshenko said she has asked Russia for help in funding the gas imports. Russian officials have said they are ready to lend Ukraine money, but only jointly with the European Union.

Ukraine has been badly hit by the global economic downturn, with its economy shrinking by 21 percent in the first quarter and its currency losing more than a third of its value against the dollar as exports dropped and investors fled emerging markets.

It has already been promised a $16.4 billion rescue package from the International Monetary Fund but must curb public spending in return.