A cabinet minister who helped lead Mexico's anti-drug fight, his deputy and seven others died in a helicopter crash in the mountains west of Mexico's capital on Wednesday. There were no survivors.

While one official aboard the craft had received death threats from a drug trafficker, authorities said the crash appeared to be an accident caused by poor visibility due to dense cloud cover.

The helicopter, carrying Public Safety Secretary Ramon Martin Huerta (search), Federal Preventive Police Chief Tomas Valencia (search), five other passengers and a crew of two, had taken off from a military parade ground in Mexico City.

The Bell 412 helicopter, which can carry up to 16 people, was headed to an event at the maximum-security La Palma (search) prison, 35 miles west of Mexico City, when it was lost in dense fog and clouds.

"They all died in the line of duty," President Vicente Fox (search) said in a televised address, his voice cracking with emotion.

The craft crashed into a wooded mountaintop about 11,200 feet high at a spot about 20 miles outside Mexico City.

"It smashed head-on into the rock," said Miguel Angel Yunez, assistant public safety secretary, who visited the crash site. "There is nothing left of the helicopter. It doesn't exist anymore."

The Interior Department said that "everything appears to indicate that this was an unfortunate accident, caused by adverse weather conditions."

Mario Martinez, a pilot who was following in another helicopter, told local media that Huerta's craft had disappeared into a dense bank of clouds and was lost to view.

Mexican media outlets began speculating within hours of the helicopter's disappearance about the possible involvement of drug trafficking groups.

The flight was on its way to a swearing-in ceremony for prison guards, the culmination of an effort to purge corrupt officials from a prison holding notorious Mexican drug gang leaders.

The prison was cordoned off earlier this year by federal troops after investigators found evidence that reputed drug lords Osiel Cardenas (search) and Benjamin Arellano Felix (search) had joined forces and were operating their networks from behind bars.

Also on the flight was Jose Antonio Bernal (search), an official from the country's National Human Rights Commission. Bernal had been threatened in the past by Cardenas, reportedly because Bernal had refused to recommend greater privileges for Cardenas at the prison.

The rights commission said the threats were reported to Huerta's agency.

Fox created the Public Safety Department after taking office in 2000, combining federal police forces overseeing prisons, highways and borders — including the Federal Preventative Police, a force that includes soldiers assigned to police work like crowd and riot control.

A trusted Fox ally, Huerta was appointed to lead the agency in August 2004.