There is hope that 31 tourists missing in Algeria are alive, German and Austrian ministers have said, amid mounting speculation that the travellers have been kidnapped.
The tourists were travelling without guides
The tourists - including 15 Germans and 10 Austrians - have all vanished on trips to the Sahara desert since early February.
The theory that they have been kidnapped has gained ground, says the BBC's Mohamed Arezki Himeur in Algiers.
The Dutch Government has reportedly confirmed that one its citizens, also missing in Algeria, has been kidnapped.
"We have confirmation that Dutchman Arjen Hilbers has been kidnapped," Foreign Ministry spokesman Hendrik Dek was quoted as saying by French news agency AFP.
"We are not commenting on the matter in the interests of the inquiry and the safety of those who have been kidnapped," he added.
Media reports in Algeria have suggested that militant groups linked to Osama Bin Laden's al-Qaeda network could be behind the disappearances.
Desert guides say they are mystified
Attention has focused on militant Islamist leader Mokhtar Belmokhtar, who operates in the region.
No ransom demands are believed to have been received.
German Interior Minister Otto Schily said on Sunday he was cautiously hopeful that all 31 missing tourists were alive.
And Austria's Foreign Minister, Benita-Maria Ferrero-Waldner, returning from a trip to Algeria, also expressed a "glimmer of hope".
Information from Algerian ministers suggested the tourists were alive as recently as 8 April, she said.
However, she warned the families of the tourists not to become too optimistic.
The missing tourists, who were in at least six or seven separate parties also include four Swiss nationals and a Swede. Some were crossing the Sahara by motorbike.
An Algerian army officer taking part in the search has said he believes the 31 people are alive, but no longer in Algeria.
"I don't think they are in Algeria, nor that they are dead or lost in the desert," he told the Algerian newspaper L'Expression.
It's as if the travellers had vanished into thin air
It was strange, he added, that no trace of the tourists' vehicles or clothes had been found, and no bodies had been recovered.
Hunts using helicopters and camels have failed to find any trace of the missing tourists.
All were travelling without guides, and had left no details of their planned routes across the Sahara.
They were in an area betwen Ouargla, Djanet and Tamanrasset.
Sahara guides say they have no explanation for the disappearances.
"It's as if the travellers had vanished into thin air," said desert guide Mouloud Hiri. "It's a mystery. The nomads we come across in the desert haven't noticed anything unusual."
Our reporter says that whatever the outcome of the search, the disappearances will hit tourism in the Algerian Sahara, which has so far escaped the violence which has hit other areas.