Mexico's president has ordered an investigation into the helicopter crash that killed Francisco Blake Mora, the country's interior minister, and seven others on Friday.

Felipe Calderon said the helicopter was flying in fog when it went down in southeast Mexico City, but all possible causes were under investigation.

"Mexico has lost a great patriot ... and I lost a dear friend," Calderon said, describing Blake, his right hand man in security matters, "an exemplary Mexican, honest, hardworking, and loyal".

In the front lines of his country's bloody war against drug cartels, Blake, 45, is the second interior minister during Calderon's term as president to be killed in an aviation accident.

The helicopter left from a military base in Mexico City at 8:45am and 10 minutes later disappeared from radar, Dionisio Perez Jacome, the country's transportation secretary, announced late on Friday.

Television images showed the scattered wreckage of the helicopter on a hillside south of the capital.

Drug war

Jacome said the government had asked US and French aviation crash experts to help in the investigation.

Mexico is locked in a brutal conflict against drug cartels that has killed 45,000 people in the last five years and Blake Mora was a prominent member of Calderon's security team.

On November 4, 2008, Juan Camilo Mourino and several other people died when their small aircraft crashed next to a major Mexico City boulevard during rush hour.

Investigators concluded that Mourino's plane had been flying too close to a much bigger jet ahead of it, on the flight path to land at Mexico City airport, possibly causing a fatal wave of turbulence.

Blake took office in July 2010, the fourth man to serve as interior minister under Calderon.

The last tweet on Blake Mora's twitter account was on November 4, when he paid tribute to Mourino.

"Today we remember Juan Camilo Mourino three years after his passing, a human being who worked towards the realisation of a better Mexico," Blake said in the tweet.

Source: Al Jazeera and agencies