US Secretary of State Condoleezza Rice arrived in Warsaw Tuesday, ahead of the formal signing of a deal on basing an American missile shield in Poland.
A plane carrying Rice and other US officials landed in Warsaw shortly before 8:00 pm (1800 GMT), for a ceremony which comes after months of negotiations coloured by strident opposition from Russia.
On Wednesday, Rice is due to meet with Polish President Lech Kaczynski and other officials, before inking the deal with Foreign Minister Radoslaw Sikorski at 11:30 am (0930 GMT).
Washington plans by 2011-2013 to base 10 interceptor missiles in Poland plus a radar facility in the neighbouring Czech Republic -- both of them NATO members -- to complete a system already in place in the United States, Greenland and Britain.
Moscow is deeply opposed to the missile plan, and the deal signing comes amid a spike in tensions between Washington and its allies over Russia's conflict with pro-Western Georgia, a country staunchly supported by fellow ex-communist Poland.
Washington insists the shield -- endorsed by all 26 NATO member states earlier this year -- is to fend off potential missile attacks by what it calls "rogue states," a phrase regarded as including Iran.
Moscow, however, considers it a security threat designed to undermine Russia's nuclear deterrent. It has threatened retaliation against the Poles and Czechs, warning they could become a target for attack.
Warsaw and Prague have had rocky relations with Moscow since they broke free from the crumbling communist bloc in 1989, and ties have worsened since they joined NATO in 1999 and the European Union in 2004.
US and Polish negotiators inked a preliminary missile shield deal in Warsaw last Thursday, capping 15 months of negotiations.
Talks had ground on until the US accepted oland's demands for extra security guarantees in return for hosting a missile base, including a Patriot missile air-defence system and boosted military ties.
The missile plan also involves the deployment of several hundred US troops in Poland to service the shield facility and Patriots missiles, which will gradually be turned over to the Poles once they have been trained to use them.
Washington and Prague had already sealed the radar deal in July.
Both accords must still be ratified by Polish and Czech lawmakers.