Homeland Security Secretary Michael Chertoff said Friday that U.S. intelligence led Mexican forces to a small submarine captured this week packed with 5.8 tons of cocaine.
Chertoff called the vessel's seizure Wednesday off Oaxaca state in southern Mexico "a great example of our cooperation."
"We shared information with the Mexican navy, but the Mexican navy acted alone in actually executing the seizure," Chertoff told a news conference in Mexico City.
• Click here for photos.
Mexican navy Vice Adm. Jose Maria Ortegon said the 30-foot green submarine was equipped with GPS and a compass, and its crew had planned to drop off its shipment on Mexican shores. The navy has since stepped up patrols in the area.
Authorities arrested four Colombian crew members who claim to be fishermen forced by drug cartels to move the cargo. They say they left the Colombian port of Buenaventura about a week ago.
Similar makeshift submarines carrying drugs have been discovered off Colombia and Central America, but the navy says the seizure is a first for Mexico.
Chertoff, who is on a three-day trip to meet with Mexican security officials, said drug cartels are increasingly relying on the subs to smuggle cocaine to the United States.
U.S. officials say traffickers use the vessels to carry about 32 percent of the cocaine moved by water from South America to the U.S.
Costing about $1 million, the boats are usually painted to blend in with the color of the water, U.S. Coast Guard Cmdr. Thad Allen told reporters in Washington on Friday.
Many are capable of carrying more than 10 tons of cocaine and can be operated by remote control from hundreds of miles away, Allen said.
Drug cartels have been looking for new ways to move drugs north to the United States as the Mexican government cracks down on drug trafficking across the country.
President Felipe Calderon has deployed 25,000 soldiers across the country to battle drug gangs, which have responded with bold attacks on the military and police. More than 4,000 people have been killed in turf wars, assassinations and shootouts since Calderon took office in December 2006.
Chertoff said Friday that a U$400 million aid package recently approved by the United States would go to help Mexico buy equipment, train agents and coordinate information with the U.S. He also praised Mexico's drug offensive.
"My personal belief is that you got to step down very hard very quickly on those people who challenge the rule of law and defy it, and that's why I'm pleased to see the Mexican military has been involved," Chertoff said. "They have been aggressive, and most of all they haven't been intimidated."