The reports say the UN observers were captured in the village of Azhara, 75km (45 miles) from the regional capital Sukhumi.

The Abkhaz Defence Minister Vladimir Minkanba told journalists in Sukhumi that unidentified gunmen had demanded a ransom for men.

It is not yet clear how many have been abducted but there are reports that at least five men were taken hostage after their helicopter landed in the mountainous region.

The observers had arrived in Georgia to monitor a truce between government forces and separatists in Abkhazia, which declared its independence from Georgia on Tuesday.

The Abkhazia parliament also called on the UN to recognise its sovereignty.

Independence referendum

One report quotes Abkhaz officials as saying the men were being held by members of the Svan minority, which is hostile to the separatist government.

Earlier this year, a referendum was held at the same time as presidential elections, in which 98% of voters were said to have supported independence.

However, correspondents say few states are prepared to recognise it. Russia - where there is some sympathy for the Abkhaz cause - has made it clear in will not recognise a separatist regime for fear of encouraging other nations within the federation to do the same.

'Terrorists'

About 150 UN observers patrol a ceasefire zone between Georgian and Abkhazia forces.

The Russian news agency Interfax said on Wednesday the kidnapping was being blamed in Abkhazia on "Georgian terrorists" .

Abkhazian separatists took control of the province in a 1992-93 war against government troops.

Peace talks have stalled over the issue of the return of more that 300,000 ethnic Georgian refugees who fled the fighting.

Members of the UN Security Council have acknowledged that there is a "continuing volatile situation in the conflict zone".