MEXICO CITY (Reuters) - Mexican Interior Minister Juan Camilo Mourino, an ally of President Felipe Calderon, died on Tuesday when a small plane he was traveling in crashed into evening rush hour traffic in Mexico City.

The reason for the crash was not clear but a civil aviation disaster expert told Reuters that sabotage could not be ruled out, along with other possible causes like engine failure.

Seven other people were killed and 40 injured when the government Learjet smashed into the street in an upscale business district of the capital, setting several cars ablaze.

Calderon, who is waging a high-stakes war on Mexico’s powerful drug cartels, mourned the loss of a close aide and friend who had worked with him for years.

“Mexico has lost a compatriot who worked for the service of his country,” Calderon said in a televised speech.

“The federal government, under my charge, in coordination with the relevant institutions, will carry out all necessary investigations in order to check in depth what caused this tragedy,” he said.

Jose Luis Santiago Vasconcelos, the deputy attorney general until recently and a key player for years in Mexico’s army-led war on drug cartels, was among other government officials who died in the crash.

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More than 4,000 people have been killed this year, mainly drug traffickers but also police and soldiers, by drug gang hitmen lashing back at Calderon’s anti-cartel campaign and fighting new turf wars with each other.

Drug gangs appeared to take their feud with the government to a new level in September when a grenade was lobbed into a crowd of civilians celebrating a national holiday. Authorities are holding three men charged with carrying out the attack for the Gulf cartel’s armed “Zetas” wing.

Communications Minister Luis Tellez said everything pointed to Tuesday’s crash being caused by an accident, but Jorge Lara, vice president of a national civil aviation rescue committee said it was too early to be sure. “It could have been anything, from mechanical failure to sabotage,” Lara told Reuters.

PLANE NOSEDIVED

A colleague of Lara at the scene said it appeared that something happened to the plane in the air and it nosedived into the ground, with minimal damage to surrounding buildings.

Mourino, who was 37 and married with three children, was a rising star in Mexican politics who helped engineer conservative Calderon’s 2006 election victory against a leftist popular with many in poorer parts of the country.

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A U.S.-educated economist and former lawmaker, Mourino was picked to head the interior ministry in January to help push Calderon’s reform agenda through the divided Congress.

Vasconcelos was a veteran police chief with a 20-year career at the attorney general’s office.

As the smoking wreckage clogged up traffic on one of Mexico City’s main thoroughfares, Mayor Marcelo Ebrard told reporters at the scene there was no way Mourino had survived.

“It’s a fact. There is no other possibility,” Ebrard said.

Mexican radio reported an air traffic controller as saying the aircraft had been coming in to land at Mexico City airport when it hit the ground between tall office buildings.

Tellez said there was no contact with the plane moments before the crash, which had been returning from a trip to the central city of San Luis Potosi.