A leader of the notorious Zetas drug cartel has been caught in Mexico City, according to Mexican authorities.
José María Guízar Valencia is wanted in the US, which had offered a $5m (£3.6m) reward for his capture.
Known as Z-43, he is a dual US-Mexican citizen and is thought to have run the Zeta's south-eastern operations.
The US state department said he was responsible for "importing thousands of kilograms of cocaine and methamphetamine to the US every year".
On its website, it said the Zetas "have murdered an untold number of Guatemalan civilians during the systematic overtake of the Guatemalan border region with Mexico during recent years".
The alleged kingpin was arrested in Mexico City's Roma neighbourhood, which is known for its hip bars and restaurants.
He was captured "without the use of force", said the head of the National Security Commission, Renato Sales, in a press conference on Friday, when the news was confirmed.
He is now likely to face extradition to the US, on drugs smuggling and money-laundering charges.
In 2012, the Zetas was considered the largest drugs gang in Mexico.
However, they have lost ground in recent years, as others, notably the Jalisco New Generation, have expanded to take their east-coast territory.
Arrests of other leaders have also weakened the group, causing internal divisions.
The group, which sprang from the Gulf Cartel, was founded by corrupt members of the military and the police.
Last year was Mexico's most violent year on record, with more than 25,000 murders.
Organised crime is thought to account for nearly three-quarters of those deaths.