The BBC's Khalid Javed: The kidnappers use foreigners as negotiating pawns

Diplomats said they were travelling in five vehicles in the southern province of Abyan when they were abducted and taken to an unknown destination.

A Yemeni guide and one British tourist are reported to have escaped.

The kidnappings come a day after tribesmen in north-eastern Yemen attacked the country's main oil pipeline, setting off a fire which is still burning.

Correspondents say Yemeni tribesmen frequently use tactics such as kidnappings and attacks on oil installations to press their demands for improved health and social services in tribal areas.

Regional aid

The kidnapping took place in the southern town of Mudiah, in the Abyan province, about 200 km (175 miles) south of the capital, Sanaa.

The BBC's Frank Gardner: Much of Yemen is "a pretty lawless place"

There was no immediate news on the demands of the kidnappers, but in the past tribesmen have demanded regional aid from the government and oil companies.

A UK Foreign Office spokesman confirmed they had received reports of the kidnapping from the British Embassy in Sanaa.

"We are in close touch with the Yemen authorities in Sanaa and London and we are seeking clarification about the incident," he said.

"We have made it clear that our top priority is the safe and swift return of the hostages."

Four German tourists abducted three weeks ago are still being held in the eastern province of Marib.

More than 100 foreigners have been abducted since 1992, but most have been well-treated and released unhurt.