President Bush said Monday the United States will help modernize the Polish military as part of an expected agreement on putting a new U.S. missile defense system in the country.

The two countries have been negotiating Polish demands for help in upgrading its military in exchange for allowing the missile defense interceptors. After meeting with Polish Prime Minister Donald Tusk in the Oval Office, Bush said the United States recognizes the need for Polish forces to be modernized, and "we're responding."

"There is a commitment to a system that respects Poland's sovereignty and that will ensure that the people of Poland will not be subjected to any undue security risks," Bush said. "This is the kind of issue that all kinds of rumors and worries can grow out of and we just want to assure people that it's necessary and at the same time there will be this modernization effort that will take place."

U.S. negotiators, led by acting Assistant Secretary of State Stephen Mull, have tried to seal the deal with Poland by opening a separate negotiating track on the Polish demands. They have sought to leave promises vague.

But Tusk seemed pleased with what he heard from Bush, saying it was significant that the missile defense program and the U.S.-aided modernization of the Polish military would be considered all in "one package."

"What I would call a breakthrough is my internal conviction that the president and the American side today very precisely understand our expectations, and if I can say, Mr. President, accept our point of view on the principle of cooperation," he said through a translator. "As the president said, the technical aspects and the tempo of talks and a couple of other issues will be on the expert level, but our common intention is unambiguous."

Neither leader talked specifics. Bush said "obviously there's a lot of work to do" and that experts are working through the details to make sure that "the people of Poland are comfortable with the idea."

"Before my watch is over, we will have come up with a modernization plan that is concrete and tangible," Bush said.

The United States opened the negotiations last year with the government of previous Polish Prime Minister Jaroslaw Kaczynski, who strongly supported the U.S. proposal. Tusk's government has sought more in return.

Polish officials have said they are looking for help to acquire air defenses against short- to medium-range missiles. Negotiators have asked for Patriot 3 or THAAD missiles and have identified 17 areas of the Polish military that the United States could help modernize. Interceptors for the planned U.S. shield are for protection against long-range missiles.

The Polish government argues the security backing is necessary because Russia has threatened to target Poland with nuclear missiles if it should allow the interceptors.

Russia opposes the U.S. plan to build part of its global missile defense system so close to Russian borders, arguing it would undermine the Russian deterrent. The United States says the system is aimed at countering a threat from Iran or North Korea and would be impotent against Russia's massive arsenal.