(Recasts, adds analyst, updates death toll with 9 on plane)

By Mica Rosenberg

MEXICO CITY, Nov 5 (Reuters) - A plane crash that killed Mexico's interior minister and closest ally, as well as his chief drug war adviser, does not appear to have been caused by sabotage, the government said on Wednesday.

Investigators examining the charred crash site and the plane's black box had found no evidence of foul play, but U.S. and British teams were called in to help the investigation.

Interior Minister Juan Camilo Mourino, the No. 2 figure in President Felipe Calderon's government, died on Tuesday when the government Learjet crashed in Mexico City, killing all nine aboard, five people on the ground and narrowly missing high-rise office buildings full of workers.

"It's a strong blow for Calderon. They've amputated his right arm," said political scientist Agustin Basave at the capital's UNAM university.

Mourino, a U.S.-trained economist and skilled former lawmaker, was named interior minister in January, taking charge of internal security a year into Calderon's bloody, army-led battle against powerful drug cartels.

Jose Luis Santiago Vasconcelos, a leading Calderon adviser in the drug war and former deputy attorney general with years of cartel-fighting experience, also died when the aircraft smashed into evening rush-hour traffic, setting cars ablaze.

Officials showed reporters radar images of the plane's trajectory as it descended toward the international airport and said they had not found signs of a mid-air explosion or evidence the pilot made emergency calls.

"Can you hear me?" an air traffic controller asked the pilot as the plane went off the radar a few minutes from landing.

SUSPICIONS OF FOUL PLAY

Analysts said that even without evidence, many Mexicans would suspect foul play in a country where fear of being a drug gang target hangs heavy over government officials.

U.S. investigators were already in Mexico City on Wednesday and three more were due to arrive from Britain on Thursday.

Luis Tellez, the transport and communications minister, said there would be a "meticulous" and "detailed" probe and it could be weeks before the cause of the crash was known.

He denied Mexican media reports that the Learjet may have been destabilized by flying too close to a bigger aircraft.

"So far, we have not detected any indications that suggest a hypothesis other than that it was an accident," he said, adding that the plane was under armed guard before it took off from central Mexico.

U.S. State Department spokesman Sean McCormack called Mourino "a valiant leader" in the joint war on drug crime.

Mexico has been tense since September, when drug gangs appeared to take their feud with the government to a new level by lobbing a grenade into a crowd celebrating a national holiday in Calderon's home city, killing eight people.

More than 4,000 people have died in drug violence this year, mainly traffickers in turf wars, but hitmen have murdered a string of police chiefs in recent months.

A dozen people were being treated for burns after gas tanks used by taco stands exploded after the Learjet crashed between office buildings in an upscale business district.

Mexico's peso weakened sharply in Asia on news of the crash but pared losses and closed 0.86 percent weaker on Wednesday. (Writing by Catherine Bremer; additional reporting by Cyntia Barrera Diaz and Adriana Barrera in Mexico City; Robin Emmott in Monterrey and Susan Cornwell in Washington, editing by Patricia Zengerle)

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