MOSCOW, November 13 (RIA Novosti) - A top Iranian military official on Friday urged Russia to honor its bilateral military contract and deliver the promised S-300 surface-to-air missiles, the Mehr news agency reported.

Gen. Hassan Firouzabadi said Russia was six months behind schedule with deliveries of advanced air-defense systems.

"Why haven't they delivered the S-300 missiles? Six months have now passed since they were supposed to deliver them," he 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 on the start of the contract's implementation since then.

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

"Russia has to fulfill the contract and not be influenced by Zionist pressure," Firouzabadi said.

A Russian government official on Thursday said Moscow would not freeze the contract as a concession to the United States.

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.

The latest version of the S-300 series is the S-300PMU2 Favorit, which has a range of up to 195 kilometers (about 120 miles) and can intercept aircraft and ballistic missiles at altitudes from 10 meters to 27 kilometers.

It is considered one of the world's most effective all-altitude regional air defense systems, comparable in performance to the U.S. MIM-104 Patriot system.

Iranian Defense Minister Ahmad Vahidi urged Russia on Wednesday to fulfill its contract on the supply of S-300 air defense systems to Iran.