The man leading the fight against the Mexican drug trade, Public security Minister Ramon Martin Huerta, has been killed in a helicopter crash.
Ramon Martin Huerta was a key ally of President Vicente Fox
He was among nine people who died when their aircraft went down in mountains near Mexico City. The cause is unclear, but the weather in the area was poor.
The head of the federal police, Tomas Valencia, was also among the dead.
Mr Huerta, a close friend of President Vicente Fox, was on his way to visit a jail when the crash happened.
The BBC's Franc Contreras in Mexico City says the loss of such senior security officials will deliver a serious blow to the government's efforts to stop the drug cartels.
The helicopter they were travelling in disappeared from radar screens on Wednesday, after the pilot reported an emergency.
Rescue crews trying locate the aircraft were initially hampered by poor weather.
But the wreckage was eventually found near a village west of the capital.
"They are heroes who lost their lives in the line of duty," President Fox said of the nine victims.
Mr Huerta, who was 48, had been leading efforts to stop a wave of drug-related violence that has killed hundreds of people this year.