Articolo su CNN.com

ALGIERS, Algeria (AP) -- Searchers using camels and helicopters equipped with heat-seeking sensors have scoured the Sahara Desert for 21 tourists, mostly Germans, who vanished in Algeria over the past six weeks.

But the search effort has, so far, been in vain, and authorities cannot even say whether smugglers, Islamic insurgents or potentially devastating desert problems like empty gas tanks are to blame.

Five groups of tourists -- 16 Germans, four Swiss and a Dutch national -- have disappeared in Algeria since the end of February.

Most went missing near desert towns such as Illizi, near the Libyan frontier, and Tamanrasset, the main town in southern Algeria, some 2,000 km from the capital.

"Authorities and the population are searching river beds, canyons and dunes, in vehicles and on the backs of camels" to try to find the tourists, said a statement issued Thursday by an association of travel agencies, known as UNATA.

Officials have also used helicopters equipped with heat-seeking sensors that could probe any sign of life beneath the sand, newspapers here have reported. The German Foreign Ministry on Thursday confirmed the use of special equipment.

The first disappearances occurred February 21, when 11 tourists -- six Germans, four Swiss and a Dutch national -- went missing somewhere between Ouargla and Djanet, in the middle of the desert, according to the official APS news agency.

It reported the disappearances only on March 17.

The latest group, two men and two women aged 45-64 from the southern German city of Augsburg, left for Algeria February 22. They were last heard from in the center of the country on March 8, Augsburg police said. One of the women had been expected to return at the end of March.

Drug traffickers
Smugglers and drug traffickers are known to haunt the area around southern Algeria, near the borders with Niger and Libya. The German Foreign Ministry warned Tuesday that criminal groups and smugglers operating in that area pose a risk and advised travelers to put off trips to the region.

Islamic extremists waging an insurgency in Algeria for more than a decade have not carried out attacks in the vast desert region.

Still, there has been speculation that insurgents may be behind the disappearances.

The press, which has paid only slight attention to the disappearances, suggested at one point that Mokhtar Belmokhtar, linked to the Salafist Group for Call and Combat, one of two main insurgency movements in Algeria, could be behind the disappearances. It linked the mysterious Belmokhtar to smugglers.

European anti-terrorism officials have tied the Salafist Group of Call and Combat to al Qaeda, the network of Osama bin Laden.

However, the group, led by Hassan Hattab, has traditionally targeted police officers, soldiers and other symbols of power, avoiding indiscriminate attacks on civilians.

The Germany Foreign Ministry spokesman, speaking on condition of anonymity, declined to comment on speculation that the Salafist Group for Call and Combat might have seized the tourists. But, he added, "We can't exclude anything."

UNATA, the travel agency association, expressed concern at the numbers of tourists who venture into the Sahara Desert without a properly planned trip or a guide.

"It is imperative to distinguish between real Sahara tourism and impromptu and clandestine expeditions," the travel association said.

Tourists have been found dead in the desert in the past, stranded because they ran out of gas.