Poland's prime minister spoke with Vice President Dick Cheney on Thursday to discuss negotiations over basing American missile defense interceptors in Poland, a government spokesman said.

The phone conversation took place a day after officials announced a tentative agreement had been reached in Washington this week. That moved President Bush closer to his goal of a global defense shield, but Polish authorities took pains Thursday to stress the deal was not final.

Government spokesmen Jacek Filipowicz confirmed to The Associated Press that Prime Minister Donald Tusk talked with Cheney for 40 minutes on the "state of negotiations," but declined to give any details.

Earlier, Tusk and Foreign Minister Radek Sikorski met with U.S. Ambassador Victor Ashe for 45 minutes. Tusk's press office said the meeting touched on Polish-U.S. cooperation, including "negotiations concerning the construction in Poland of the missile defense shield."

The U.S. plan calls for 10 missile interceptors to be based in northern Poland as part of a global defense system that Washington says is aimed at deterring long-range missile attacks by "rogue" states like Iran.

The Kremlin has objected strongly to the idea of putting interceptor missiles in Poland and a tracking radar in the Czech Republic, saying the system would weaken the deterrent power of Russia's missile forces.

Czech leaders have agreed in principle to the plan, but the Czech parliament still must approve the deal. Polish officials, meanwhile, are insisting on a big boost in U.S. military aid for serving as a missile base, and they sought Thursday to play down the tentative agreement.

Speaking on Radio Zet, Defense Minister Bogdan Klich said that "negotiations have not finished" and stressed that Poland had not made a final decision on whether to host the U.S. base.

"Our final stance and that of the prime minister depends on the security balance" of the project, Klich said. "If it turns out that our demands have been met at an appropriate level, ... then yes. If it turns out that ... the costs outweigh the benefits — then no."