A land mine exploded under a U.S. vehicle south of Kabul (search) on Saturday, killing four soldiers in the deadliest incident for American troops in Afghanistan in almost 10 months, the military said.

The blast highlighted the dangers still facing foreign and Afghan troops more than three years after the fall of the Taliban (search), although there were conflicting accounts about whether the mine was freshly laid or left over from Afghanistan's long wars.

A Taliban spokesman claimed responsibility for the blast. But U.S. spokeswoman Lt. Cindy Moore (search) said investigators suspected the mine was an old charge dislodged by recent rain and snow or that the vehicle had wandered into an unmapped minefield.

"We believe it was an old mine which could have shifted," she said.

The victims were among a group of American and Afghan officials scouting a potential site for a shooting range in Logar Province, 25 miles south of the Afghan capital, when one of their three vehicles hit the mine, Moore said.

The bodies of the four dead, none of whom was identified, were airlifted to the main U.S. base at Bagram, Moore said.

About 17,000 U.S. troops are in Afghanistan battling a stubborn Taliban-led insurgency focused on the south and east and training the new Afghan army. The U.S. military says its air and ground operations have killed eight suspected militants and four civilians in the past week alone.

According to U.S. Department of Defense statistics, 122 American soldiers have died since American forces invaded to oust the former Taliban government for harboring al Qaeda militants after the Sept. 11, 2001, attacks on the United States.

Many have been killed in accidents, including strikes on old mines left behind by Soviet troops who occupied Afghanistan in the 1980s or the Afghan factions including the Taliban who fought each other after the Soviets withdrew.

Moore said U.S. troops had first toured the scene of Saturday's incident about a week earlier in search of a site for a training range for the Afghan army.

Gov. Mohammed Aman Hamini said the incident occurred in a desert area crisscrossed by rough tracks.

"It's an old mine. There's no traffic on the route they took, but the Russians used to use it because they were afraid of the main road," Hamini told The Associated Press.

However, Mullah Hakim Latifi, a man who claims to speak for the Taliban, said its fighters detonated the mine by remote control.

"We've said again and again that we would resume our holy war in the spring," Latifi told AP by satellite telephone from an undisclosed location.

Also Saturday, Uruzgan Gov. Jan Mohammed Khan said U.S. forces detained two suspected Taliban militants the day before as they tried to plant a remote-controlled mine on a road in the province.

The blast Saturday was the deadliest incident for the U.S. military since May 29, 2004, when four American special forces soldiers were killed in Zabul province, near the Pakistani border, reportedly by an intentionally laid mine.

The bloodiest incident was an accidental explosion at an arms dump in Ghazni province that killed eight American soldiers in January last year.