The Russian navy has sunk a Georgian boat armed with missile launchers, according to reports.

The news came as fighting continued to rage in and around the disputed border region of South Ossetia despite Georgia's claim it had called a halt to the hostilities.

Witnesses reported hearing at least 15 explosions in the region after a ceasefire was supposed to come into effect.

A bomb dropped by a Russian plane exploded near the main civilian airport in the Georgian capital Tbilisi hours before French Foreign Minister Bernard Kouchner flew in to try to mediate an end to the conflict.

There were also reports that Russian jets bombed a military airport on the outskirts of Tbilisi as part of a wave of attacks outside South Ossetia.

Moscow earlier said its forces took control of Tskhinvali, the capital of the breakaway republic, following three days of heavy fighting.

Russian forces poured into the pro-Russian province after Georgia began attacking separatists - a move the Kremlin denounced as "genocide".

Russian warships were said to be near Georgian waters and Tbilisi claimed Russian troops had launched an operation in Abkhazia, another separatist region.

Both provinces won de facto independence from Georgia and want to join the Russian Federation.

The US has said it will offer a UN Security Council resolution condemning Russian military action against Georgia as "unacceptable to the international community".

The White House criticised Russia after it bombed at least three Georgian targets outside South Ossetia and claimed the Kremlin was interested in "regime change" in Georgia.

State-controlled Russian television has spoken of a "humanitarian catastrophe" in South Ossetia, with more than 2,000 dead and thousands homeless.

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