Arms maker Almaz Antei has delivered 15 batteries of S-300 anti-aircraft missiles to China, Interfax reported Friday, under a contract that analysts said could be worth as much as $2.25 billion.

China is a major buyer of Russian weapons, and the two countries say they are trying to forge a strategic partnership, though senior Russian officials are privately concerned about an increasingly assertive China.

Russia has delivered 15 S-300 batteries to China, said Igor Ashurbeili, director general of Almaz Antei, which makes the missiles, Interfax reported.

"We have implemented a contract to deliver to China the newest system S-300," Ashurbeili said. He gave no details about the value of the deal. A spokesman for the plant was not immediately available for comment.

In Russia's armed forces, an S-300 battery normally consists of four truck-mounted installations, each with four missiles held in metal tubes.

Analysts said the contracts to deliver the S-300 to China were signed in the mid-2000s and that each battery usually costs about $120 million to $150 million. That indicates that the value of the Chinese contract was about $1.80 billion to $2.25 billion.

"The price for one S-300 battery varies between about $120 million and $150 million," said Konstantin Makiyenko, deputy head of the CAST defense think tank.

The S-300, known in the West as the SA-20, can shoot down cruise missiles and aircraft. The missiles have a range of at least 150 kilometers and travel at more than two kilometers per second.

Russian arms exports rose to a post-Soviet record of $8.5 billion last year, with Algeria, India and China accounting for two-thirds of deliveries. Syria, Venezuela, Malaysia and Vietnam accounted for another 20 percent of deliveries.

Moscow has said it plans to fulfill a contract to supply the S-300, nicknamed "the favorite" in Russia, to Iran, unnerving Israel and the United States.

The possible sale to Tehran of the S-300, which could protect Iran's nuclear facilities against air strikes, has become a sensitive issue in Russia's relations with Israel.

Russia has a more advanced air defense system, known as the S-400 "Triumph," and Ashurbeili said the country's armed forces were expected to receive the third battery of these "any day from now."

A senior Russian general said last year that Moscow was now developing a fifth-generation, surface-to-air missile, the S-500, which would be able to implement the tasks of both air and space defense.

Officials have said the new system would be capable of engaging ballistic hypersonic targets flying at a speed of five kilometers per second.