Mexico’s military has notched an important success for President Felipe Calderon with the arrest of Jorge Eduardo Costilla Sanchez, the reputed boss of the powerful Gulf drug cartel.

Costilla, nicknamed “El Coss,” was captured without a fight in the coastal city of Tampico, in the border state of Tamaulipas, Navy spokesman Jose Luis Vergara said Thursday.

Wednesday’s arrest — together with the seizure of weapons, vehicles and jewels — is a much needed achievement for Calderon, whose offensive against drug cartels has done little to stem drug-related violence or the volume of drugs transported through Mexico.

The mustachioed Costilla, handcuffed and wearing a checkered long-sleeve shirt under a bulletproof vest, was presented before reporters.

Mexican marines chased a vehicle of armed men into a residence in Tampico, where they “surprised” Costilla and arrested him, Vergara said.

Costilla is said to head a criminal group considered the third-most powerful in Mexico.

“El Coss is an important actor,” said George Grayson, professor of government at the College of William & Mary and expert of drug cartels. “His capture is a tremendous blow to the Gulf cartel.”

Five others were arrested with Costilla, and of five more of his bodyguards were arrested after a shootout in a separate city, Vergara said. Some of them wore camouflage uniforms when they were presented next to Costilla.

There are rewards in Mexico and the United States for Costilla’s arrest.

Costilla has been indicted in the United States, accused of drug trafficking and threatening U.S. law enforcement officials in November 1999.

In that incident, according to the U.S. State Department, Costilla and other suspected Gulf Cartel leaders allegedly stopped federal agents and pointed AK-47 rifles at them. The agents were allowed to leave after a standoff.

The State Department offered a reward of up to $5 million for information leading to Costilla’s arrest. In Mexico, where Costilla is on the government’s list of the 37 most-wanted traffickers, officials offered more than $2 million for his capture.

While not as powerful as it once was, the Gulf Cartel is one of Mexico’s major drug trafficking organizations.

Costilla assumed a top role after the arrest of former Gulf Cartel boss Osiel Cardenas Guillen and became the top leader after a rift with Cardenas’ relatives in the organization, authorities have said.

As Costilla rose in the cartel hierarchy, the group controlled smuggling routes in northeastern Mexico by using its enforcement arm, known as Los Zetas, authorities have said. But Los Zetas later split into its own violent cartel, and for several years has been fighting the Gulf Cartel for the lucrative turf.

“El Coss survived internal divisions and directed violent confrontations in Tamaulipas and Nuevo Leon against his former allies, Los Zetas,” Vergara said.

The arrest is the latest in a series of blows against the Gulf Cartel, based in the city of Matamoros, across the border from Brownsville, Texas.

This month, Mario Cardenas Guillen, reputed leader of the Gulf faction loyal to the Cardenas family, was also arrested by the military.

Costilla’s arrest was the result of “intense intelligence” work by the Navy, and information gleaned from Mario Cardenas’ arrest, Vergara said.

The rival Zetas, who operate in the same northeastern part of the country, may seem poised to take advantage of their rival’s vulnerability.

But Grayson says internal divisions within the Zetas will prevent them from turning the heat up on the Gulf cartel, and that the Sinaloa cartel will be the trafficking group most likely to strengthen its position.

The other big winner is the Mexican navy and its marines, who are responsible for the biggest arrests against top-level traffickers, he said.

In the past, surges in violence have been recorded after the killing or capture of cartel bosses. Internal rifts within the Gulf cartel and Zetas could lead to fights and alliances in a “kaleidoscope situation,” Grayson said.