PARIS—Four skiers were killed and another injured in an avalanche in the French Alps on Friday and their guide was held for questioning, authorities said.

The group of six people was on a ski touring expedition in an off-trail area near Entraunes, close to the Italian border in the southern Alps.

The identities of the skiers were not immediately released. Prosecutor Jean-Michel Pretre of Nice said in remarks shown on French television that they were “seniors,” all with experience in backcountry skiing. He said the guide knew the area well.

A judicial inquiry was opened into manslaughter and involuntary injury, and the guide was taken in for questioning, the prosecutor said.

The cause of the avalanche was unknown. French authorities had warned against a high risk of avalanches in the Alps following heavy snowfall in recent days, and the prosecutor called that “a decisive element.”

The Mountain Guides Union said the group was in a non-steep area of the Mercantour national park. In a statement, the union said the guide was also buried by the avalanche but managed to get out.

An avalanche farther north in the French Alps on Friday killed a 25-year-old woman at La Grave, according to local media reports.

More than a dozen people have died in avalanches in the French Alps this ski season, in addition to those killed in other parts of the mountain range.

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