(CNN) -- Mexican authorities have captured a suspected leader of the Gulf cartel, officials said Tuesday.
A man who "is presumed to be and says he is" Mario Cardenas Guillen was detained Monday in the northern state of Tamaulipas, a spokesman for Mexico's navy told reporters.
His brother, Osiel Cardenas Guillen, was the cartel's founder and former leader. A U.S. federal judge sentenced him to 25 years in prison in 2010 after he pleaded guilty to five felony charges, including conspiracy to possess with intent to distribute, conspiracy to launder money and threatening to assault and kill federal agents.
Mario Cardenas Guillen, also known as "M1" and "The Fat One," became one of the cartel's top leaders that year, after another brother was killed in a Mexican military operation, officials said.
Authorities had previously accused him of helping to run aspects of the cartel's operation while he was in a Mexican prison on organized crime charges.
From inside prison, authorities said he operated an auto body workshop that outfitted cars with compartments used to transport cocaine and marijuana to the United States. He was released from prison in 2007.
On Tuesday, Vice Adm. Jose Luis Vergara Ibarra, a spokesman for Mexico's navy, said Mario Cardenas Guillen was connected with a number of pending cocaine trafficking cases.
The Gulf cartel is one of Mexico's major drug-trafficking organizations. It is based in the Mexican city of Matamoros, across the border from Brownsville, Texas.
The cartel split into two factions after its former leader, Antonio Cardenas Guillen -- also known as Tony the Storm -- was killed in a military operation in 2010, Vergara told reporters Tuesday.
Authorities announced the arrest of Mario Cardenas Guillen a day after Mexican President Felipe Calderon defended his drug war strategy in his final state of the union speech.
More than 47,500 people have been killed in drug-related violence across Mexico since Calderon deployed federal troops to combat cartels shortly after taking office in December 2006. The Mexican government has not released official statistics since January, and others estimate a much higher death toll.
On Monday, Calderon blamed fighting between rival cartels for the violence.
"Federal intervention has not been the problem. It has been part of the solution," he said.
Calderon, who will leave office when his term ends in December, urged Mexico's next government to continue the fight against organized crime.