Kabul, Afghanistan ? A U.S. military helicopter returning from a mission smashed into the southern Afghan desert Wednesday, killing at least 16 people in the deadliest military crash since the fall of the Taliban in late 2001. An Afghan official said most of the dead appeared to be Americans.

The CH-47 Chinook was returning to the U.S. base at Bagram from a mission in the militant-plagued south when it went down near Ghazni city, 80 miles southwest of the capital, Kabul.

“Indications are it was bad weather and that there were no survivors,” said a U.S. spokeswoman, Lt. Cindy Moore. An Afghan official said there were no signs the craft was shot down.

A U.S. military statement said 16 deaths had been confirmed and two other people listed on the flight manifest were “unaccounted for” when the recovery operation was suspended at nightfall.

U.S. officials said the four crew members killed were Americans, but declined to give the nationalities of the passengers. The names of the victims were being withheld pending notification of next of kin.

Moore said the transport helicopter was returning from a routine mission.