SALANG PASS, Afghanistan — Dense fog forced rescuers to search on foot for the wreckage of an Afghan passenger plane carrying 44 people, including six foreigners, that crashed today in mountains north of Kabul, officials said. There was no immediate word of casualties.

The British embassy in Kabul confirmed that three British citizens were on the plane, but did not identify them. One American also was on board, a State Department official in Washington, D.C., said on condition of anonymity pending notification of family. The nationalities of the two other foreigners were not immediately available.

Seventy rescue workers were searching on the ground as dense fog covered the area of the crash near the 12,700-foot-high Salang Pass, a major route through the Hindu Kush mountains that connects the capital to the north.

“The only way they can search is on foot,” said Col. Nabiullah, who is in charge of the southern portion of the Salang Pass. “The helicopters can’t get in.”

The plane, operated by Pamir Airways, a private Afghan airline, was flying from the northern city of Kunduz to the capital, said Mohammad Asif Jabar Khil, police chief at Kabul’s international airport. It crashed about 60 miles from Kabul, he said.

At the request of the Afghan government, NATO dispatched a fixed-wing aircraft to the last known position of the plane.

Capt. Robert Leese, a spokesman for the NATO air unit assisting in the search, said the U.S. plane got within four miles of the crash site, but had to turn back because of bad weather.

“The fog was so bad you couldn’t tell where the mountain began and the fog ended,” Leese said.

Other NATO helicopters were on standby at Bagram Air Field and at the Kabul airport to assist in any rescue effort, NATO said in a statement. The Afghan Defense Ministry also ordered the nation’s air force to be on standby.

Jaweed Stanikzai, the brother of a passenger on the plane, told The Associated Press at the Kabul airport that he last talked to his brother at 8 a.m.

“He told us that he was on the plane and could not talk, but would call us as soon as he could,” he said. “Nobody is providing us any information about the incident.”

Deputy Transportation Minister Raz Mohammad Alami, who was traveling to the crash site with the minister of aviation and other officials, said the plane was carrying 44 people, including six foreigners and six crew members.

Mohammad Azim, chief of police in the Jabalussaraj district of Parwan province, said the crash occurred between his district and Shotul in Panjshir province.

Ismail, a 35-year-old snowplow driver who lives in a village near the pass, said he was taking a morning break when he heard the sound of a crash.

“It was as if there was an accident of two vehicles. I didn’t know what it was,” said Ismail, who only goes by one name.

Kabul-based Pamir Airways started operations in 1995. It has daily flights to major Afghan cities and also operates flights to Dubai and Saudi Arabia for the hajj pilgrimage.

According to its website, it uses Antonov An-24 type aircraft on all its Kunduz-to-Kabul flights.

Pamir’s chief executive officer, Amanullah Hamid, said the plane was last inspected about three months ago in Bulgaria.

The An-24 is a medium-range twin-turboprop civil aircraft built in the former Soviet Union from 1950 to 1978. Although production there ceased more than three decades ago, a modernized version is still being made in China.

It is widely used by airlines in the developing world due to its rugged design, ease of maintenance and low operating costs. It is designed to operate from remote, unprepared airstrips with austere navigational aids.

A total of 143 have so far been lost in all sorts of accidents, according to the Aviation Safety Network’s statistics.