Militants have released images purporting to show the tourists
More than a month after their disappearance, the fate of two Austrian hostages who were captured while touring the Tunisian desert remains shrouded in uncertainty.
But the case has been seen to expose the difficulty of controlling the vast expanses of the Sahara as al-Qaeda's North Africa affiliate seeks to make its presence felt across the Maghreb.
The group, which was blamed for a number of spectacular suicide bombings in Algeria last year, has raised its profile once more after claiming the kidnapping.
It is now thought to be holding Wolfgang Ebner, 51, and Andrea Kloiber, 43, at an undisclosed location in northern Mali.
According to statements posted on the internet, the kidnappers have demanded that militants held in Algeria and Tunisia be freed in return for the release of the Austrians.
They have twice deferred a deadline, stating most recently that their request must be met by 6 April.
There have been unconfirmed reports that the group is also asking for a ransom.
The al-Qaeda Organisation in the Land of the Islamic Maghreb (AQIM) emerged from the remnants of the Islamist insurgency that began in Algeria in the 1990s.
It adopted its current name early last year as - after years of being worn down by the Algerian security forces - it began to scale up bombings and increase its flow of propaganda.
But recent attacks had been largely restricted to northern Algeria.
Jean-Francois Daguzin, a senior research fellow at the Foundation for Strategic Research in Paris, said that last month's kidnapping showed the group was trying to spread its influence, drawing together smaller militant factions from across the region.
"The desire is to create an insurrectional space, and to attract attention by targeting foreigners," he said.
The case of the Austrians is not without precedent.
Between February and May 2003, a group of militants from the Salafist Group for Call and Combat - AQIM's precursor - captured 32 European tourists travelling across the Sahara and held them for several months.
One of the hostages is reported to have died of heat exhaustion, before the militants released the last of the tourists in August of that year after reportedly receiving a ransom of 5m euros from the German government.
German officials refused to confirm or deny the reports.
That incident focused attention on the security threat in the Sahara, and prompted efforts to tighten controls.
The US government had identified the Sahel area, which borders the Sahara desert and including Mali, Niger, Chad and Mauritania as a potential terrorist haven, setting up the Pan-Sahel Initiative as a counter measure.
This developed into the expanded Trans-Saharan Counter Terrorism Initiative, which also covers Algeria, Morocco, Tunisia, Senegal and Ghana.
The programme is "designed to help develop the internal security forces necessary to control borders and combat terrorism and other illegal activity," according to the US military.
Although some observers have questioned how great the radical threat in the region really is, the disappearance of the Austrian tourists appears to show that there are still gaps along the porous desert borders.
"The Sahara is a dangerous place if only because various groups recognise that the states don't exercise a monopoly on power," said Geoff Porter, an analyst for the Eurasia Group in New York
"They can't, they don't have the capacity."
Senior Austrian diplomat Anton Prohaska has been sent to Bamako
But he said that there were still questions about how the kidnappers had transported the Austrians across hundreds of kilometres of desert, some of which are militarised, and it was possible that regional governments had facilitated the transfer of the hostages to neutral ground.
The Austrian authorities say they are still not clear about exactly where the two tourists, who last contacted their relatives on 18 February, had disappeared.
Once it was reported that they were being held in Mali, they dispatched a team of emissaries to the capital, Bamako, where there is no Austrian embassy.
Austria's government has been seeking help as it tries to get to handle a complex case in unfamiliar terrain.
"We established contacts with governments, NGOs, individuals, and people who are knowledgeable about the area," said Peter Launsky-Tieffenthal, a spokesman for the Austrian foreign ministry.
"It's really a major effort involving all sorts of parties in the region and beyond."
There have been unconfirmed reports that Saif al-Islam Gaddafi, son of the Libyan leader Muammar Gaddafi, is one of those involved in negotiations.
Last week there was also an outbreak of violence in northern Mali as Tuareg rebels, who are seeking more autonomy and a greater share of resources across the region, attacked a Malian army convoy.
The Austrians are thought to be in the remote desert of northern Mali
Austrian authorities say they have no indication that the unrest has affected the kidnap case, but they are following the situation closely.
In one of their statements, the kidnappers warned Western tourists not to visit Tunisia and other North African countries, including Morocco, Algeria and Mauritania.
A photograph released in conjunction with the statement shows a woman - said to be Ms Kloiber - wearing a blue headscarf with her face digitally obscured.
This may be because showing a woman's face is prohibited under radical Islamist beliefs.
The case is particularly worrying for Tunisia, which has a thriving tourist industry.
Apart from a suicide attack in 2002 on the island of Djerba, the country has been largely successful in keeping a lid on Islamic extremism.
Austria has raised its travel warning for the south of Tunisia, though the foreign ministry noted that most tourism is directed to the Mediterranean coast in the north.
"Tunisia has always been the safest country in the Maghreb," said Mr Daguzin.
"This shows that despite all their efforts to show that there is complete security, AQIM is able to strike wherever it wants."