The visit by Sergei Kislyak was at the invitation of Polish Foreign Minister Radoslaw Sikorski, who said Saturday there were no guarantees of the missile shield's installment as he saw no direct threat emerging from Iran -- an argument Washington makes in supporting the missile system.

Polish Prime Minister Donald Tusk said following his November election that Poland has "no rigid doctrine regarding the deployment of a U.S. missile defense base in the country," and said the issue was "open for all arguments for and against," RIA Novosti said Wednesday.

The United States wants to deploy missile interceptors in Poland and a radar installation in the Czech Republic to thwart Iran and other "rogue" states. Russia says the missile shield offsets the strategic balance of forces in the region and threatens national interests.