More than half of the 32 European tourists missing in Algeria have been found alive, but the fate of the four kidnapped Swiss remains unknown.
The foreign ministry said on Wednesday it had no knowledge of where the Swiss nationals might be.
The ministry added it had decided to send two more experts from the Federal Police Office to Algeria to assist the two Swiss officials already in the country since April.
Seventeen people have so far been freed - ten Austrians, six Germans and one Swede.
"We do not know anything about what has happened to the four Swiss or their whereabouts at the moment," said Simon Hubacher, a spokesman for the foreign ministry.
Hubacher added that he regretted that the other countries had publicly announced that their nationals had been found.
"The lives of those still missing in Algeria could be endangered [by these announcements]," he said.
Justice Minister Ruth Metzler confirmed at a press briefing that an operation to free some of the hostages had taken place.
The Algerian army said commandos had freed the 17 tourists, who were being held by the Salafist Group for Preaching and Combat (GSPC).
The GSPC is thought to be an Islamic extremist group, with links to the al-Qaeda terror network.
The Algerian media reported that the kidnapped tourists had been split up into separate groups and speculated that the remaining hostages were being held in the Sahara's Illizi region.
The foreign ministry said on Monday that it believed the four Swiss were still alive.
The Austrian and German governments have refused to comment on the circumstances of their nationals' release but said the Austrians were already on their way home and the Germans were in the capital, Algiers.
The four Swiss have been missing since February after heading into the Sahara desert without a guide.
swissinfo with agencies
Four missing Swiss tourists are not among the 17 hostages who have been freed in Algeria.
Among those freed were ten Austrians, six Germans and one Swede.
The whereabouts of the Swiss nationals are still unclear.
The four Swiss have been missing since February when they set off into the Sahara desert without a guide.
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