Former Mexican defense minister Salvador Cienfuegos has been arrested in the United States on undisclosed charges, Mexico's foreign minister said Thursday. 

Cienfuegos, who was defense chief from 2012-2018, was reportedly on a trip with his family when he was detained at Los Angeles airport.

"The consul in Los Angeles will inform me of the charges in the next few hours. We will offer the consular assistance to which he is entitled," Foreign Minister Marcelo Ebrard said on Twitter.

The Mexican investigative magazine Proceso, quoting unnamed sources at the US Department of Justice, reported that the arrest was the result of a long-standing investigation into corruption involving drug traffickers.

The Wall Street Journal, quoting an unnamed senior Mexican government official, said Cienfuegos was arrested at the request of the US Drug Enforcement Administration (DEA).

There was no immediate confirmation from the US authorities.

Cienfuegos, 72, headed the defense ministry under former president Enrique Pena Nieto.

According to Mexican media reports, he was detained by US authorities when he arrived on a trip with his family.

Mexican prosecutors did not immediately respond to requests for information about why Cienfuegos was arrested.

During Pena Nieto's presidency, some members of the armed forces faced accusations by human rights groups in connection with the case of 43 students who went missing in 2014 in a case that shocked the country.

More than 296,000 people have been murdered since the government militarized the fight against the drug cartels in 2006, according to the authorities, who say most of the killings are linked to gang violence.

While defense minister, Cienfuego complained about his troops having to take part in the country's war on drug trafficking, saying the military was not suited for the job.

"We didn't ask to be here. We don't like it. We didn't study how to chase criminals," he said.

"Our function is something else and it's been made into something unnatural. We are doing things that don't correspond to our training because there's no one else to do them," the minister said.

Cienfuegos is the second former Mexican minister who is detained in the United States.

Ex-public security minister Genaro Garcia Luna was arrested in Texas in December 2019 on charges of taking huge bribes to allow the notorious Sinaloa cartel to ship drugs into the US.

Garcia Luna, an architect of Mexico's war on drug trafficking, pleaded not guilty.