Foreign Minister Ahmed Aboul Gheit said in New York that the group was captured by "gangsters." He did not say how he knew of their release, or whether a ransom was paid.
The five Germans, five Italians and one Romanian were seized Friday along with their Egyptian guides and drivers while camping near the Sudanese border, Egyptian Tourism Minister Zoheir Garana said. Government spokesman Magdi Rady said it was feared the kidnappers had taken the captives into Sudan.
Only a few intrepid visitors make the daunting trek of more than a week in 4X4s across the desert to the Gilf, which lies near Egypt's borders with Libya and Sudan beyond a vast plain of dunes known as the Great Sand Sea. It is one of the most arid places on Earth.
Gilf al-Kebir has become increasingly popular among adventure and eco-tourists drawn by the stark desert landscapes and the prehistoric paintings in caves that dot the plateau. They include the "Cave of the Swimmers," immortalized in the 1996 movie "The English Patient." The cave features 10,000-year-old paintings of people swimming, a hallmark of a time when scientists believe parts of the Sahara were covered by lakes and rivers.
The unpopulated region is a crossroads for ethnic African tribesmen - including smugglers - from Libya, Sudan and even Chad, further south. It borders Sudan's Darfur region, where raging conflicts have given rise to armed bandits who have become notorious for robberies and hijackings.
Rady said the abduction was not connected to Islamic militants, who have previously attacked tourists in southern Egypt and the Sinai Peninsula. "This is a criminal act. They are seeking a ransom," he said.
Garana said the tour company that organized the trip negotiated with the kidnappers, who demanded up to $6 million in ransom. He said the German government was involved in the talks but the Egyptian government was not. Germany's Foreign Ministry said only that it had formed a "crisis team" on the abduction.
The kidnapping was only discovered because the Egyptian owner of the tour company, who was on the trip, was able to call his German wife by mobile phone, Garana told state television. The group included eight Egyptians, he said.
The tour owner told his wife that a group of armed men, who appeared "African," drove up to the group while they were setting up their tents, an Egyptian security official said, speaking on condition of anonymity because he is not authorized to talk to the media. It was not clear when that phone call took place.
Italy's Foreign Ministry said the owner called his wife in Cairo again on Monday night and told her their captors had taken the group to Sudan.
The kidnapped Italians included three women and two men from the Turin area, Italy's ANSA news agency said.
A tour guide who operates in the area said colleagues in the Western Desert told him the kidnappers were tribesmen. Mohammed Marzouk said there have been previous robberies in the area, most recently in May, when tribesmen seized two tour company SUVs during a desert trip.
Tourism is Egypt's biggest foreign currency earner. The industry was devastated in the 1990s when Islamic militants waged a campaign of violence, including attacks on tourists. The campaign was suppressed in a fierce crackdown by the government of President Hosni Mubarak and the industry has since been rebuilt.
Since 2004, attacks on foreigners shifted to the beach resorts of the Sinai peninsula in northeastern Egypt, with a total of 121 people, including tourists, killed in a series of bombings.
But there have been no major attacks in the capital, Cairo - home of the Pyramids - or the main antiquities sites in the south in more than a decade. There have been no known Islamic militant attacks in Egypt's Western Desert, where the Gilf al-Kabir is located.
The Gilf al-Kabir, some 550 miles southwest of Cairo, is one of the last frontiers in Egypt, explored by a few Egyptian and European expeditions in the early 20th Century. The Cave of the Swimmers was discovered in a niche in the cliff face in 1933 by Hungarian explorer Laslo Almasy. Since then, the Gilf has largely been ignored until it gained the recent notice of adventure travelers.
The Gilf is a giant limestone and sandstone plateau - bigger than Delaware or the island of Cyprus and nearly 300 meters (1,000 feet) high at some points. It is separated from the rest of Egypt by a vast sea of sand dunes.
The plateau is creased with wadis, or dry river valleys, producing dramatic landscapes of dunes washing up against high black cliff faces. The wadis are pockmarked with caves holding one of the richest troves of Neolithic cave art in Africa. Rock faces are covered with red and black paintings of lions, gazelles, bullocks, giraffes and people hunting, as well as silhouettes of hands. Tour guides still boast of discovering new cave paintings.
Tourists are required to get permits from the military to visit the site and must travel in tour groups with at least one security guard. The tour, done in desert 4X4s, can take more than 12 days.
But, as in other places, expanding adventure tourism may be moving closer to zones of instability. Earlier this year, the annual Dakar Rally through the Western Sahara was canceled because of al Qaeda threats of attacks.