Some of the 31 European tourists feared kidnapped in Algeria have left a message in the desert saying they are alive, an Austrian spokesman has said.
The tourists were travelling without guides
The message said "We are alive", said the Austrian Foreign Ministry's Thomas Buchsbaum, who has responsibility for finding the 10 missing Austrians.
The tourists - also including 15 Germans, four Swiss nationals, a Dutchman and a Swede - have all vanished on trips to the Sahara desert since early February.
"I am optimistic," said Mr Buchsbaum, who stressed there was no evidence to confirm a kidnapping.
The Dutch Government, however, announced that its missing citizen had been kidnapped.
We have confirmation that Dutchman Arjen Hilbers has been kidnapped
Dutch Government spokesman
"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.
The theory that the Europeans have been kidnapped has been gaining ground, says the BBC's Mohamed Arezki Himeur in Algiers.
The tourists were in six or seven separate groups, and were all travelling without guides. Some were crossing the Sahara by motorbike.
Desert guides say they are mystified
Media reports in Algeria have suggested that militant groups linked to Osama Bin Laden's al-Qaeda network could be behind the disappearances.
Attention has focused on militant Islamist leader Mokhtar Belmokhtar, who operates in the region.
No ransom demands are believed to have been received.
Further details of the desert message have not been revealed, but Austrian officials say it was left on 8 April.
The message's location has enabled police - currently searching a huge expanse of desert region - to focus their hunt.
Both German and Austrian ministers have said they have hope that the missing tourists are still alive.
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".
However, she warned the families of the tourists not to become too optimistic.
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 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.