Russia is still considering the possible deliveries of advance air defense systems to Iran and will not freeze the contract as a concession to the United States, a government official said.

Russia signed a contract with Iran on the supply of S-300 air defense systems to the Islamic Republic in December 2005. However, there have been no official reports about the start of the contract''s implementation since then.

"The issue of S-300 deliveries [to Iran] is still under discussion. There are some technical and other problems," said Konstantin Biryulin, deputy director of the Federal Service for Military-Technical Cooperation.

The possible deliveries of S-300 missiles to Iran have aroused serious concern in the West and in Israel.

The official denied media speculations that Russia could freeze the Iranian contract in exchange for Washington''s decision not to place interceptor missiles in Poland and a missile tracking radar in the Czech Republic.

"I do not understand why there is so much media frenzy over the deliveries of S-300 to this region...Russia has the right to decide on its own whether to deliver these systems to any country which is not under the UN Security Council''s sanctions," Biryulin said.