Russia says it has deployed S-300 anti-aircraft missiles in the breakaway region of Abkhazia in Georgia.
The Georgian government - which refuses to acknowledge Abkhazia's independence - says it is "concerned" by the move.
The announcement comes just days after an unscheduled visit by Russian President Dmitry Medvedev to the region.
Russia recognised Abkhaz independence in 2008 after winning a brief war with Georgia over nearby South Ossetia.
In a statement released by the Russian government, air force commander-in-chief General Alexander Zelin said the role of the missiles would be "anti-aircraft defence of the territory of Abkhazia and South Ossetia".
"We have deployed the S-300 system on Abkhaz territory, which, alongside other aircraft defence systems of the ground forces, will solve the problems of air defence of the territories of Abkhazia and South Ossetia," he was quoted as saying.
The self-styled Abkhaz foreign minister, Maxim Gvinjia, later contradicted Gen Zelin, telling the BBC that the general's statement on the S-300s had been "misinterpreted".
But Sergey Shamba, the breakaway region's prime minister, later told the BBC that the missiles were in Abkhazia, and had already been there for about a year.
A spokesman for the US state department also said the missiles appeared to have been in place for some time.
"It is our understanding that Russia has had S-300 missiles in Abkhazia for the last two years," said the spokesman, PJ Crowley. "We can't confirm whether they have added to them or not."
Georgia's Deputy Prime Minister Temur Yakobashvili expressed anxiety over Russia's statement.
"This should be of concern not only for Georgia but also for other regional actors including Nato," he told the AFP news agency.
"It is very obvious that Russia is using these occupied territories as a military platform for larger plans than only Georgia".
The BBC's Richard Galpin in Moscow says that one theory among Russian experts is that Russia is trying to warn Nato and the US not to help Georgia rebuild its air force.
The air force only amounts to about half a dozen planes and a few helicopters, and Moscow may be trying to show that its sophisticated weaponry would be more than able to deal with any expansion.
The second anniversary of the brief war in 2008 has been used by the Russian government to emphasise its ties with the breakaway regions.
During his recent visit to Abkhazia, Mr Medvedev reiterated Russia's support for its independence and promised more financial aid.
Last year Russian Prime Minister Vladimir Putin announced that Moscow would pay for part of the region's defence infrastructure.
In August 2008, fighting in Georgia's breakaway region of South Ossetia escalated into war between Georgia and Russia.
Russian forces quickly drove Georgian troops out of first South Ossetia then Abkhazia before a peace deal was signed.
However so far only Venezuela, Nicaragua and the tiny Pacific island of Nauru have joined Russia in recognising the independence of the two regions.
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