Warsaw, Poland ? Poland and the United States struck a deal Thursday that will strengthen military ties and put an American missile interceptor base in Poland, a plan that has infuriated Moscow and sparked fears in Europe of a new arms race.

“We have crossed the Rubicon,” Polish Prime Minister Donald Tusk said, referring to U.S. consent to Poland’s demands after more than 18 months of negotiations.

Washington says the planned system, which is not yet operational, is needed to protect the U.S. and Europe from possible attacks by missile-armed “rogue states” like Iran. The Kremlin, however, views it as aimed at Russia’s missile force and warns it will worsen tensions.

U.S. officials also said the timing of the deal was not meant to antagonize Russian leaders at a time when relations already are strained over the recent fighting between Russia and Georgia over the South Ossetia region.

In an interview on news channel TVN24, Tusk said the United States agreed to help augment Poland’s defenses with Patriot missiles in exchange for placing 10 missile defense interceptors in the eastern European country.

He said the deal also includes a “mutual commitment” to come to each other’s assistance “in case of trouble.”

That clause appeared to be a reference to Russia, which has threatened to aim its nuclear-armed missiles at Poland – a former Soviet satellite – if it hosts the U.S. site.

In past days, Polish leaders said the war justified Poland’s demands that it get additional security guarantees from Washington in exchange for allowing the anti-missile base on its soil.

But after the deal was announced, both American and Polish officials sought to play down any connection to the Georgian war.

“This is not linked to the situation in Georgia,” the chief U.S. negotiator, John Rood, told The Associated Press, after the pact was initialed. “We had made these arrangements for this round of negotiations before the conflict in Georgia.”

The Pentagon has stressed that the 10 interceptors planned for Poland are not designed to counter Russia’s huge missile arsenal but to defend against emerging threats from countries such as Iran. Pentagon leaders have pushed to move as quickly as possible to implement the agreement, in light of the recent missile tests by Iran.

According to a senior defense official, the U.S. will base one Patriot missile battery in Poland along with about 100 U.S. military personnel to support it. The associated costs would be shared to some degree by both countries, said the official, who spoke on condition of anonymity because the agreement has not yet been formally signed.

The Patriot will come from a battalion in Germany.