TEHRAN, Iran —  Russia is selling Iran a new and sophisticated air defense system that experts say is capable of dealing a serious blow against would-be attackers.

The new S-300 air defense system signals growing miitary cooperation between Moscow and Tehran, Iranian Defense Minister Mostafa Mohammad Najjar said Wednesday.

"The S-300 air defense system will be delivered to Iran on the basis of a contract signed with Russia in the past," state television quoted Najjar as saying.

Najjar didn't say when or how many of the S-300 anti-aircraft missile defense systems would be shipped to Iran.

Earlier this year, Russia delivered 29 Tor-M1 air defense missile systems to Iran under a $700 million contract signed in December 2005.

Russian officials wouldn't comment on the Iranian statement, but the Interfax news agency quoted an unidentified source in the Russian military-industrial complex as saying that a contract for the missiles delivery had been signed several years ago and envisaged the delivery of several dozen S-300 missile systems.

The S-300 is much more powerful and versatile weapon than the Tor-M1 missile systems supplied earlier, which were capable of hitting airborne targets flying at up to 20,000 feet.

The S-300 is capable of shooting down aircraft, cruise missiles and ballistic missile warheads at ranges of up to 95 miles and at altitudes of up to 90,000 feet. Russian military officials boast that it excels the U.S.-built Patriot missiles currently being deployed in Israel.

Rumors about the sale of S-300 missile systems to Iran have circulated for a long time, but Russian officials consistently denied it.