Russian news agencies cited a top defense official Wednesday as confirming that a contract to sell powerful air-defense missiles to Iran was signed two years ago, but saying no such weapons have yet been delivered.

Russian officials have consistently denied claims the country already has provided some of the S-300 missiles to Iran. They have not said whether a contract existed.

The state-run ITAR-Tass and RIA-Novosti news agencies and the independent Interfax quoted an unnamed top official in the Federal Military-Technical Cooperation Service as saying the contract was signed two years ago. Service spokesman Andrei Tarabrin told The Associated Press he could not immediately comment.

Supplying S-300s to Iran would change the military balance in the Middle East and the issue has been the subject of intense speculation and diplomatic wrangling for months.

Israel and the U.S. fear that, were Iran to possess S-300 missiles, it would use them to protect its nuclear facilities — including the uranium enrichment plant at Natanz or the country's first atomic power plant, which is now being built by Russian contractors at Bushehr.

That would make a military strike on the Iranian facilities much more difficult.

It was not clear why the missiles have not been delivered, but the reports cited the defense official as saying "fulfillment of the contract will mainly depend on the current international situation and the decision of the country's leadership."

That could indicate that Russia intends to use the contract as a bargaining chip before next month's meeting between President Dmitry Medvedev and President Barack Obama.

But the defense official said Russia does not intend to abandon the contract, estimated to be worth hundreds of millions of dollars, ITAR-Tass said,

A prominent Russian analyst, Ruslan Pukhov of the Center for Analysis of Strategies and Technologies, said the missile contract was seen by the Kremlin as primarily a political rather than commercial matter.

"The S-300 contract, and cooperation with Iran in general, is regarded by Moscow only as an instrument of political bargaining with the West and not as a way of realizing the fundamental defense and commercial interests of Russia," he was quoted as saying by RIA-Novosti.