More than 2 1/2 tons of cocaine was seized last week in the eastern Pacific Ocean by the crew of the Charleston-based Coast Guard cutter Dallas, officials said Friday.

The estimated 5,250 pounds of cocaine was confiscated aboard an 82-foot fishing vessel flying the Mexican flag in international waters south of Panama, officials said.

The drugs were discovered concealed in a hidden compartment built into the boat's fuel tanks, the Coast Guard said.

The advanced method of concealment required a detailed search of the vessel that lasted three days and included shifting the vessel's fuel load to identify the hidden compartment, officials said.

The operation was conducted under the authority and jurisdiction of Mexico.

The Mexican Navy subsequently dispatched a vessel to take custody of the boat, contraband and crew, all of whom are Mexican nationals, officials said.

"This seizure is an example of the cooperation and collaboration between the U.S. and Mexico, as both nations work together to combat illicit drug trafficking," said Lt. Cmdr. Rick Foster, spokesman for the Eleventh Coast Guard District in Alameda, Calif.

The Dallas has a crew of 167 who carry out homeland security, search and rescue and law enforcement missions from New England to Central and South America.

In February the 378-foot Dallas left Charleston for Port-au-Prince, Haiti, where it joined the global humanitarian relief effort after an earthquake rocked the island, killing more than 200,000 people.

When Russia invaded the country of Georgia in 2008, the Dallas was the first ship to bring in humanitarian supplies.

Last year, the cutters Dallas and Gallatin moved to Detyens Shipyards on the Cooper River for up to $15 million in repairs. Though designed to last 25 years, both ships entered service more than 40 years ago.

Officials noticed problems with the Gallatin after it finished a counter-drug patrol off the coast of Colombia. The Dallas returned from deployment in Africa, the Mediterranean and the Black Sea looking even worse.

Holes from corrosion let water seep into compartments over the years, wearing down major structural components of the ships.

The cutters also need mechanical repairs to piping and ventilation systems, antennae and weapons systems.

The improvements could tack another decade onto the cutters' service lives, officials said.