He was detained in the street, seemingly eating or buying an ice-cream

Estuardo Mario Bermudez

He is said to be the right-hand man of Osiel Cardenas, the alleged kingpin of the Gulf drug cartel.

Mr Medrano is also wanted in the US on suspicion of threatening narcotics agents in Texas.

The Gulf cartel allegedly smuggles cocaine and other drugs across the Texan border.

Mexico is a key transport route for illicit drugs travelling from South America to the US.

Adan Medrano, also known as "El Licenciado", faces charges in Mexico of smuggling cocaine and attempted murder.

He was carrying a gold-plated 38-caliber pistol when agents from Mexico's Federal Agency of Investigation closed in on him, but the arrest was made without a shot being fired.

At the time of his capture, the suspect was in the company of a woman and a juvenile.

"He was detained in the street, seemingly eating or buying an ice-cream for the juvenile," Mexico's special drugs attorney Estuardo Mario Bermudez told a news conference.

Mr Medrano has been moved to a jail in Mexico City.

Mr Bermudez said the attorney general's office was requesting that he be transferred to a maximum security prison.

FBI

According to the FBI, on the 9 November 1999, an FBI agent and a Drug Enforcement Administration agent were driving a vehicle with diplomatic licence plates in Matamoros when they stopped by Osiel Cardenas, Mr Medrano and several other heavily armed men.

The gang allegedly tried to remove the agents from the vehicle at gunpoint, repeatedly threatening to kill them. Eventually, the agents were allowed to continue their journey, the FBI said.

US authorities had offered a $2m reward for information leading to Mr Medrano's arrest.

Benjamin Arellano was arrested earlier this month

They want him extradited to the United States to face charges for allegedly assaulting the two agents, in addition to charges of possession and intent to distribute more than 100 kilograms of marijuana.

Mr Bermudez described Adan Medrano's capture as a major setback for the Gulf cartel.

"It weakens substantially the structure of the cartel of Osiel Cardenas," he said.

Earlier this month another of Mexico's most wanted drugs-trafficking suspects, Benjamin Arellano Felix, was arrested in the city of Puebla.