Mexico's top federal law enforcement officer, a longtime ally of President Vicente Fox who led the war against a rising tide of national violence, was killed Wednesday along with eight others in a helicopter crash.

Ramon Martin Huerta, secretary of public security, was traveling to a ceremony for new prison guards at Mexico's maximum-security La Palma prison when the Bell 412 helicopter crashed into a wooded mountain about 20 miles west of the capital, authorities said.

"I profoundly regret the terrible accident," Fox said in a nationally televised address Wednesday night. "I have lost an associate, but above all, a dear friend."

Bad weather and poor visibility caused the pilot to crash into the rocky hillside, according to a preliminary assessment by government officials. The helicopter did not carry voice or flight data recorders, officials said.

Rescue worker Juan Carlos Cruz Martinez said fog appears suddenly in the mountains of San Miguel Miniapa, where the helicopter crashed sometime before noon. It took several hours to find the wreckage.

"It was destroyed completely, completely," he said. "When we got there, around 6:30 p.m., there was still white smoke coming out from the aircraft. . . . The guys from the defense department wouldn't let us get close. They told us they were investigating."