KABUL, Afghanistan - A U.S. military helicopter returning from a mission smashed into the southern Afghan desert Wednesday, killing 13 American military personnel and three U.S. government contractors in the deadliest military crash since the fall of the Taliban in late 2001, the military said.

Two other U.S. service members were unaccounted for, spokeswoman Lt. Cindy Moore said today. The nationalities of the three contractors were not immediately available.

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," Moore said. An Afghan official said there were no signs the craft was shot down.

Moore said the transport helicopter was returning from a "routine mission" when controllers lost radio contact. A second Chinook made it safely back to the sprawling base north of Kabul.

Associated Press Television News footage showed dozens of Afghan security forces and officials scurrying around burning wreckage. Strong winds that had whipped thick dust into the darkened sky fanned the flames.

Abdul Rahman Sarjang, the chief of police in Ghazni, said the helicopter crashed about 2:30 p.m. near a brick factory three miles outside the city and burst into flames. U.S. troops rushed to cordon off the area, he said.

Sarjang said the weather was cloudy with strong winds and that witnesses reported one of the helicopter's two rotors looked damaged before it hit the ground. He said he saw no sign of enemy fire, and militants issued no claim of responsibility

According to U.S. Department of Defense statistics, at least 122 American soldiers had died before Wednesday's incident in and around Afghanistan since the U.S.-led war on terrorism began after the Sept. 11, 2001, attacks.

The previous worst incident in Afghanistan was an accidental explosion at an arms dump in Ghazni province that killed eight American soldiers in January 2004.

Most recently, four U.S. soldiers died when a land mine exploded under their vehicle south of Kabul on March 26.

In November, six Americans - three civilian crew members and three U.S. soldiers - died when their plane crashed in the Hindu Kush mountains. The military's last fatal helicopter crash occurred a month earlier when a pilot was killed in the west of the country.

About 17,000 U.S. soldiers are in Afghanistan battling a Taliban-led insurgency and training a new Afghan army.