(Reuters) - The U.S. Coast Guard has suspended its search indefinitely for three recreational fishermen who disappeared after their boat capsized in rough seas over the Fourth of July holiday weekend off Hawaii, an official said on Friday.

The fishermen were reported missing late on Sunday when they failed to return to port at Heleiwa, on the north shore of Oahu, and the following day the Coast Guard found their 20-foot (6-metre) vessel, upside down about 25 miles (40 km) off the island.

The Coast Guard-led search for the three crewmen covered 27,600 square miles (71,484 square km) and involved an HC-130 Hercules airplane, patrol boats, helicopters and jet skis, the federal agency said in a statement.

"Suspending searches is the hardest thing to do in the Coast Guard," Petty Officer Tara Molle, a spokeswoman for the agency, said by telephone.

The decision was made late on Thursday after all efforts had failed to find any sign of the fishermen, but the search could resume if any new lead develops, Molle said.

The Coast Guard extended its condolences to the families of the missing fishermen, who were identified as Jensen Loo, Clint Oshima and Derek Tomas, all in their 30s.

The Coast Guard has said it was unclear how the boat capsized, but at the approximate time of the incident winds of 15 to 25 miles per hour (24-40 kph) were reported, along with waves 8 feet (2 meters) high.

(Reporting by Alex Dobuzinskis in Los Angeles; Editing by Steve Gormanm and Sandra Maler)