Mexico on Friday admitted it had mistakenly claimed to have captured a son of Mexico's most wanted drug lord, Joaquin "Shorty" Guzman, which the ruling party had hailed as a major victory in its war on cartels.

Mexican marines seized the man on Thursday outside Guadalajara and flew him to Mexico City, where they paraded him in front of the media and identified him as Jesus Alfredo Guzman, alias "El Gordo" or "The Fat One."

The man's lawyer, Veronica Guerrero, told a news conference earlier on Friday her client's real name was Felix Beltran and that he was an innocent car dealer.

The federal attorney general's office said late on Friday the man arrested was indeed Mr Beltran, without giving any further details.

The mix-up is a major embarrassment for the government, which has been heavily criticised for failing to contain the violence and flow of drugs since president Felipe Calderon sent in the military to fight the cartels shortly after taking office in December 2006.

Marines said they apprehended the man with an arsenal of rifles, pistols and grenades and about $160,000 in cash.

Javier Oliva, a political scientist from the National Autonomous University of Mexico, said the snafu showed how poor the coordination is between US intelligence agencies as well as their cooperation with Mexican counterparts.

"This is really serious. Nothing like this has ever happened before," he said, wondering how the agencies had gone public on the arrest without making the proper checks.

"The main responsibility here lies with the DEA."

Thursday's arrest won praise from the US Drug Enforcement Administration, which has sought Jesus Alfredo Guzman since he was indicted for cocaine trafficking in 2009.

His father, the elder Guzman, faces dozens of charges of racketeering and drug smuggling in US courts. There is a $US5 million reward for his capture.

The arrest came just over a week before Mexicans vote for a leader to replace Mr Calderon, whom the constitution bars from seeking a second term. Brutal clashes between drug cartels and Mexican authorities have killed more than 55,000 people since Mr Calderon launched his crackdown on the gangs.

"This is confirmation that president Calderon's strategy doesn't work," said Alberto Islas, a security expert at consultancy Risk Evaluation.

He said the botched arrest demonstrated the weakness of Mexico's own intelligence apparatus.

The candidate of Mr Calderon's National Action Party, Josefina Vazquez Mota, is running in third place in most polls, partly because of public dissatisfaction over the drug war.

Reuters