Polish and US negotiators signed a deal yesterday to host parts of Washington's global missile shield system in the European Union's biggest ex-communist member.
The deal was signed by deputy Polish Foreign Minister Andrzej Kremer and US chief negotiator John Rood, a Reuters reporter present at the signing ceremony said.
Consequently parts of the US global missile shield will be placed on Polish soil, government sources said.
The sources said that under the deal, US negotiators also agreed to Polish demands for greater military cooperation in return for Warsaw's consent to host the installation.
"This agreement will include a declaration of US military cooperation in case of a threat to Poland from third states," one source said after two days of talks in Warsaw.
The agreement comes after nearly two years of tough negotiations and was clinched amid tension between the United States and Russia over the crisis in Georgia.
The deal will now have to be endorsed by the Polish Parliament, the sources said.
Russia has vehemently opposed US plans to place 10 interceptor rockets in Poland and a giant radar in the Czech Republic, saying the installations would upset the post-Cold War balance of power in Europe.
Moscow has threatened to take retaliatory steps against Poland and the Czech Republic, its former vassals in central Europe which are now part of the European Union and Nato.
In the face of Russian opposition, Polish Prime Minister Donald Tusk had argued Poland could not agree to the shield unless the United States agreed to boost Polish air defences and enhance mutual military cooperation.
Russia's military action against Georgia strengthened the argument, Mr Tusk said on Tuesday, ahead of the latest round of talks this week.
The Polish sources said the improved US offer included the stationing of Patriot batteries and a permanent presence of US military personnel in Poland.
"In real terms, this (agreement) means a permanent stationing of Patriots in Poland and, by 2012, a permanent American army base," one source said.