Thirty-one European tourists who vanished in the Sahara Desert are being held hostage by terrorist groups, a ranking Algerian official said Wednesday.

The official said the tourists had been located by the Algerian army. Some 5,000 Algerian troops and 300 local guides were brought in to track down the tourists.

The tourists, who had set off in seven separate groups on four-wheel drive vehicles or motorcycles, disappeared starting in mid-February. None had employed guides.

The tourists — 15 Germans, 10 Austrians, four Swiss, one Dutch and a Swede — are being held in the region of Illizi (search), some 810 miles southeast of Algiers near the Libyan border, the official said on condition he not be named.

"They are alive and are being held in several groups separated geographically," the official told The Associated Press.

The official refused to comment on the identities of the captors or to say whether they might belong to an Islamic extremist group. But he called them "terrorist groups," the term used to refer to Islamic insurgents.

There has been speculation that Islamic rebels battling Algeria (search)'s military-baked government for more than a decade might be behind the disappearances even though the Sahara region has been free of attacks.

No one has claimed responsibility for the disappearances, and there has been wide speculation about who might be behind them.

A name that regularly surfaces in the press is Mokhtar Benmokhtar (search), an Islamic insurgent thought to be a trafficker in arms, vehicles or cigarettes in the vast desert region between Algeria, Niger, Mali and Mauritania.

The official said the Algerian Army envisaged using force to free the captives, but German authorities balked out of fear for the safety of their citizens.

The German Interior Ministry refused to comment on the report. Foreign Ministry spokesman Walter Lindner said Wednesday that German and Algerian authorities are in constant contact.