An agreement on the status of U.S. troops on Polish soil, known as the SOFA deal, will be not signed on December 10 as expected, a Polish Defense Ministry spokesman said on Wednesday.

He did not say why it would not be signed Thursday or indicate when it could be signed.

According to the Status of Forces Agreement, U.S. troops will service Patriot missiles that are to be integrated into Poland's national security system.

The accord was given the final backing by Polish Prime Minister Donald Tusk Friday.

The first troop rotation to service the Patriot missile system was expected to arrive in Poland by the end of March 2010.

In September, U.S. President Barack Obama shelved the previous administration's plans to place 10 long-range ground-based interceptor missiles in Poland and a fixed-site radar station in the Czech Republic.

Due to a reassessment of the threat from Iran, Washington announced a new scheme for a more flexible system, with a combination of land and sea-based interceptors based on the Standard Missile interceptor, SM-3.

Under the new plan, the U.S. would place ship-based SM-3s in the North and Mediterranean seas in 2011, and mobile land-based SM-3s in Central Europe by 2015.

In contrast to the previous system which was strongly opposed by Russia, the new multidirectional radars and missiles would not be able to penetrate deep into Russia's territory. However, Russian officials have voiced concerns over the new plans as well.

WARSAW, December 9 (RIA Novosti)