Without a Trace

Algeria's southern Sahara has long been known as the stamping grounds for bands of smugglers, drug runners and a fundamentalist Islamic group with ties to al Qaida. But the region has largely been spared from the unrest and violence that have rocked the rest of the country since the outbreak of civil war in 1992.

It is also the last place contact was made with as many as 29 Europeans whose tour groups began to vanish in February.

The tourists -- 16 Germans, eight Austrians, four Swiss and one Dutch citizen -- had been on adventure vactions touring the desert on motorbikes and four-wheel drive vehicles, and were traveling in six different groups. Several groups disappeared on Feb. 21, according to the wire service Reuters, and contact was lost with another on March 17. Last week, the Austrian Foreign Ministry confirmed that a group of eight Austrians failed to board a boat that was due to bring them back to Europe via Tunisia.

Kidnapped or lost?

The Arab press is hawking several theories about the groups' disappearance. The most compelling is that they were kidnapped by Islamic fundamentalists. Another popular rumor, advanced by the Algerian newspaper Quotidien d'Oran, is that they could have gotten lost if the United States scrambled the Global Positioning Satellite systems the tourists had been relying on to navigate the desert because of the Iraq war. The groups also could have had vehicle problems in the desert's extreme conditions.

"We still can't rule anything out," a spokeswoman for Germany's Foreign Ministry said on Monday. "We're following every lead."

The search continues

For weeks, Algerian crews have used camels, planes and helicopters to search the region, but they haven't turned up any clues. Intense sandstorms have dusted the region in recent days, and investigators have used night-vision goggles and heat-seeking sensors in order to detect people. The sheer vastness of the region, which comprises 2 million square kilometers (772,200 square miles), has also slowed search efforts.

The most bizarre twist in the case came over the weekend as search teams scouring the Sahara discovered a network of cave complexes beneath the desert floor near the Libyan border.

But Switzerland disputed the significance, saying that the extensive web of tunnels was nothing new and that organized crime bands in the area have long used them.

European units join search

Now, worried European investigators have joined Algerian police in the search for the missing tourists.

Austria has already sent two diplomats and two commandos from its special Cobra unit alongside two diplomats to aid Algerian officials in the search. On Monday, Germany dispatched five agents from the Federal Office of Investigation to join them. Both countries’ foreign ministries have issued travel warnings for southern Algeria, including the cities of Djanet, Tamanrasset and Illiuzi.

The father of one of the missing tourists said his son was traveling with experienced desert trekkers. "They're being held somewhere," Manfred Notter from Besigheim, Germany, told the news agency dpa. "I believe they have been kidnapped under a political motive. All three are experienced 'desert foxes.' "

Algeria has been racked by violence since 1992, when military-backed authorities canceled a general election that radical Islamists were poised to win. The government says more than 100,000 have been killed since then, although independent sources put the figures much higher.