From IMDB:

While on a mission in Afghanistan, French captain Antarès Bonassieu’s men start vanishing one by one without explanation.

Netflix sent me a DVD of this French film with optional English subtitles.

Every now and then I happen upon a film that I cannot characterize and “Neither Heaven Nor Earth”, which held my attention every second, is such a film. Although it follows a group of French soldiers posted in the mountains of Afghanistan, it is not a military film as such. Although the central theme is the mysterious disappearances of some of the soldiers (at various times), it is not a mystery story which concludes with the solution. Because the presentation is so low-key and natural, neither does the film feel like science fiction.

Most of all the film is a study of the negative effects of the pressures of war upon soldiers, especially when those pressures are compounded by the unsolved disappearances of the four men. Go into this film without expecting any answers and enjoy the wonderful acting, the lack of cheap horror effects, and the portrayal of fear as it affects the sanity of some of the men.

One of the best reviews was provided by Roger Ebert. Another supporting review comes from Avclub.

Consider this film a well-done “happening” and keep an open mind.