United States Secretary of State Condoleeza Rice is in Warsaw to sign a deal with Poland to install part of the US missile defence system on Polish soil.
The US says having missile interceptors in Poland will help to protect against long-range missile attacks from what it calls "rogue elements" in the Middle East.
However, Russia sees the US missile interceptors as a threat to its security, and one Russian general recently warned that Poland was running the risk of a nuclear strike by hosting the base.
