The deployment of the S-300s drew immediate protest from Georgia. The Foreign Ministry called it an "extremely dangerous and provocative step that presents a threat not only to the Black Sea region but to European security as a whole."
The U.S. State Department, however, said the missile deployment was old news.
"It is our understanding that Russia has had S-300 missiles in Abkhazia for the last two years," spokesman P.J. Crowley said. "We can't confirm whether they have added to them or not."
Following a brief war against Georgia in two years ago, Russia has steadily increased military ties with Abkhazia and another breakaway Georgian republic, South Ossetia. Earlier this year, both republics agreed to allow Russia to establish military bases on their territory with up to 1,700 troops stationed at each base.
The commander of Russia's air force, Gen. Alexander Zelin, said the S-300s were intended to protect Abkhazia's air space and provide for the security of the republic, Russian news agencies reported. He said a different air defense system has been deployed in South Ossetia.
Zelin did not specify the type of S-300s deployed in Abkhazia. The advanced version is capable of shooting down aircraft, cruise missiles and ballistic missile warheads at ranges of over 90 miles (150 kilometers).
Temur Yakobashvili, the Georgian government minister in charge of issues related to the breakaway republics, said the missile system violated the cease-fire agreement that ended the August 2008 war.
The missiles' deployment was "directed not so much against Georgia as against NATO and the U.S., which intend to place their own missile defense system in Eastern Europe," Yakobashvili told The Associated Press.
The Georgian Foreign Ministry urged the international community to take decisive measures to pressure Russia to stop its "militarization" of the disputed territories and abide by the terms of the cease-fire.
Associated Press writers Misha Dzhindzhikhashvili in Tbilisi, Georgia, and Desmond Butler in Washington contributed to this report.