Javier Arellano Felix was allegedly using an alias

At its height, the so-called "Arellano Felix Organisation" is thought to have been the main supplier of cocaine and marijuana to the US.

Mr Arellano Felix was arrested on a boat in a joint US-Mexican operation off Mexico's Baja California peninsula.

Washington had offered a reward of $5m (�2.6m) for his capture.

"Javier was one of the most ruthless thugs that was involved in drug-trafficking around the world," said Michael Braun, chief of operations of the US drug enforcement administration.

"We feel like we've taken the head off the snake here."

US Deputy Attorney General Paul McNulty said the suspect had been caught on Monday morning after a tip that he was aboard the boat.

He was found by the US Coast Guard travelling under an alias, he added.

Family business

Mr Arellano Felix's arrest will be seen as a significant setback to the organisation that is believed to behind more than a 100 drug-related murders, the BBC's Duncan Kennedy reports from Mexico City.

Despite its business-sounding acronym Afo, the Arellano Felix Organisation was no faceless capitalist enterprise, our correspondent says.

It was very much a family-run affair: seven brothers and four sisters who took on the organisation in 1989.

Each sibling had his or her position and Benjamin Arellano Felix assumed the role of cartel boss until his arrest in 2002.

Then there was Ramon, who was said to organise the murders of rivals. He himself was shot dead four years ago.

The family even ran its own counter-espionage system, our correspondent adds.

It used scanners and other devices in several Mexican cities to try to keep one step ahead of the law enforcement agencies.

Crime wave

The US justice department said the cartel had recruited, trained and armed bodyguards to protect its leaders.

They also violently despatched rival drug-traffickers, police officers and journalists who printed unfavourable stories.

The task of dismantling the group was not helped by disagreements over extradition, our correspondent notes.

The Mexican authorities were opposed to capital punishment and wanted guarantees from the Americans that those arrested wouldn't be given the death penalty if sent back to the US.

Though the capture of Javier Arellano Felix is a blow to drug-traffickers, the current wave of extreme drug-related violence in Mexico shows any power vacuum is already being filled by those intoxicated by the lure of big money, our correspondent says.