The freed hostages appeared tired, but in good health
Concern is mounting over the fate of 15 European tourists still being held captive in the Sahara desert, following the release of another group of hostages on Wednesday.
The Algerian Interior Ministry said intense searches were under way to find and free the remaining hostages which, it said, were being held by "a second terrorist grouping".
Ten Austrians, six Germans and a Swede flew home on Wednesday, after Algerian troops reportedly rescued them from the hideout of an Islamic militant group near the desert town of Tamanrasset.
Their respective governments have been refusing to reveal details of the operation because of fears this might compromise the safety of the second group.
Fear of revenge
Algerian Foreign Minister Abdelaziz Belkhadem condemned what he called "media exploitation" of the rescue, saying it could "greatly interfere with the rest of the operation".
"We dare hope the rest of the hostages are freed and can rejoin the first group alive," he said.
But officials and relatives have said they are concerned about the 10 Germans, four Swiss and the Dutchman who disappeared over two months ago.
"The tourists were freed by force, not by negotiation, which means the outlook for the rest isn't good," the Reuters news agency quoted one diplomat as saying.
Andreas Mitko, whose father Witek has been missing since 8 March, expressed similar fears after the release of the first group.
"What is positive for their families makes things even worse for the other hostages.
"If it really was a military raid, then the other kidnappers could take revenge on the remaining hostages - my father, for example," he said.
A total of 32 adventure tourists were travelling without guides in a number of groups using four-wheel drive vehicles and motorbikes when they disappeared between mid-February and mid-March.
German and Swedish captives arrived at a military base in Cologne, Germany, on Wednesday afternoon.
One hostage gave a victory sign as he walked down the steps, while others appeared to be tired, leaning on the handrail but nevertheless in good health.
SALAFIST GROUP FOR PREACHING AND COMBAT
Wants Islamic state in Algeria
One of most hardline groups fighting government
On US list of "terrorist groups"
Grew out of Armed Islamic Group (GIA) around 1998
Meanwhile, a plane carrying the 10 Austrian tourists landed in Salzburg, where their relatives waited on the tarmac before embracing them as they walked down the plane steps.
One of the Austrians told German TV station RTL that the kidnappers had kept them constantly on the move as they felt Algerian troops on their trail.
"We were on the run every night... we were at the end of our physical limits, we couldn't do it anymore," Gerhard Wintersteller said.
The Algerian army said the tourists had been kidnapped by the Salafist Group for Preaching and Combat (GSPC), an Islamic group allegedly linked to Osama Bin Laden's al-Qaeda network.
It said the foreigners had been freed after an assault by government forces on a hideout of the group on Tuesday, and that all the necessary precautions had been taken to avoid putting the lives of the remaining captives at risk.
The Algerian daily newspaper El Watan reported that nine kidnappers were killed in the dawn raid near Tamanrasset, 1,900 kilometres (1,200 miles) south of Algiers.