A conversation between pilots and the control tower gave no hint that anything was wrong moments before a plane carrying Mexico's second-most-powerful official suddenly dived into rush-hour traffic.

The death of Interior Secretary Juan Camilo Mourino was a serious setback for Mexico's U.S.-backed fight against drug smuggling. He was President Felipe Calderon's most trusted confidante as the government pursues a hardline strategy that has brought down top drug kingpins but has fueled brutal violence in Mexico.

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Authorities said Wednesday that the crash, which killed 14 people in all, was mostly likely an accident. But they brought in U.S. and British investigators to help them rule out the possibility of an attack.

But the lack of evidence didn't stop Mexicans from blaming drug cartels, which have killed several top officials in recent months. That speculation contributed to a 1.3 percent drop of Mexico's peso Wednesday, according to Meg Browne, senior currency strategist with Brown Brothers Harriman & Co. in New York.

Officials played a recording of the final conversation between the control tower and the flight crew of the government Learjet 45, which was on an approach to Mexico City's airport. They calmly discussed radio frequencies and speed until the tape went silent, just as radar lost the plane's altitude reading.

Mexico City Attorney General Miguel Angel Mancera said all nine people aboard the plane and five on the ground were killed when the government jet slammed into a major avenue in the posh Lomas de Chapultepec neighborhood, igniting a fireball that lit up the evening sky. Dozens of cars caught fire and at least 40 people were injured, including a Frenchman and a Venezuelan.

U.S. Homeland Security Secretary Michael Chertoff called Mourino a "a good friend and close counterpart" and lamented the loss of "a courageous and strong partner in the fight against dangerous criminal groups."

Also killed was former anti-drug prosecutor Jose Luis Santiago Vasconcelos, who had been the target of at least one assassination attempt. Drug cartels have increasingly been targeting Mexican security officials, and the Sinaloa cartel is suspected in the death of the acting Mexican federal police chief in May.

"There are just so many coincidences, the fact that there were so many important people on the plane. It seems like it could have been an attack," said Oscar Villaruel, a 30-year-old architect staring at a newspaper's images of the fiery crash as he got his shoes shined.

Mexicans speculated about a possible attack on Internet bulletin boards, and even San Luis Potosi Gov. Marcelo de los Santos, who accompanied Mourino to the airport, said Mexicans were "waiting for confirmation that it was an accident, that it no way it was sabotage."

Officials tried to dampen any doubts.

"There are no indications that would support any hypothesis other than that this was an accident," said Transportation Secretary Luis Tellez, though he added: "We will investigate until all possibilities have been exhausted."

Tellez said the plane was under constant security before taking off from San Luis Potosi, where the officials had attended an event, and there were no indications that the 10-year-old craft had exploded or caught fire in flight.

He said the crash could have been caused by a mechanical failure, and investigators were analyzing the black box to confirm that.

Keith Holloway, the spokesman for the U.S. National Transportation Safety Board, also said there was no indication of foul play.

Experts from his agency and from the U.S. Federal Aviation Administration flew to Mexico on Wednesday, and Tellez said three experts from Britain's Civil Aviation Authority would help as well.

Meanwhile, Calderon named Deputy Interior Secretary Abraham Gonzalez as the temporary replacement for Mourino, who at 37 had been a rising star in the ruling National Action Party.

Gonzalez inherits the challenge of convincing Mexicans that the government is gaining the upper hand on cartels despite surging violence. In Tijuana alone on Wednesday, seven people were killed.

Two of the victims were beheaded, and their bodies appeared to have been dissolved in acid.