Opposition protesters stormed the presidency in Abkhazia overnight in what the leader of the Georgian breakaway region called a coup attempt.
Abkhazia is recognised only by Russia. Its capital, Sukhumi, is on the Black Sea coast.
Interfax said opposition groups took over the presidency overnight following a protest by about 1,000 people, forcing Alexander Ankvab to flee.
"I haven't left, I am still in Abkhazia," Ankvab said. "The security forces remain loyal to the state and are taking measures to stabilise the situation."
The defence minister, interior minister and chairman of the security forces released a joint statement condemning the use of "unconstitutional methods, which lead to destabilisation of the situation in the country".
"Escalation could lead to catastrophic consequences for the state," the statement said.
Ankvab was believed to have fled to his home region in northwestern Abkhazia.
The Abkhaz parliament was set to hold an extraordinary session to discuss the situation.
Ankvab was elected leader of Abkhazia in 2011 after the death of Sergei Bagapsh, who had led the breakaway region from 2005.
With the exception of Russia and a handful of far-flung states, the rest of the world still regards Abkhazia as part of Georgia.