Venezuelan authorities are holding a U.S.-flagged cargo vessel in the port city of Maracaibo and have arrested the ship's captain, an American diplomatic source told Efe on Friday.

"The captain (a U.S. citizen) is detained and the crew is still aboard" the Ocean Atlas, the source said, adding that Venezuelan authorities have offered no official explanation.

U.S. consular officials were sent to Maracaibo to look into the matter.

Asked about media accounts linking the ship to arms smuggling, the source pointed out that vessels transiting dangerous areas often carry weapons for self-defense.

The skipper of the Ocean Atlas was taken to the headquarters of Venezuela's Sebin intelligence service, Maracaibo newspaper Panorama said Friday on its Web site.

The Venezuelan government has issued no official statement on the incident and an Interior Ministry source consulted by Efe had no information.

The case of the Ocean Atlas comes a month after Venezuela detained a U.S. citizen who, according to President Hugo Chavez, admitted to having served with the Marines and appeared "to be a mercenary."

That individual remains in Venezuelan custody, the U.S. diplomatic source said.

"We don't have more information. We have consular access, we have access to him and he is detained in Caracas," the source told Efe, explaining that the individual has withheld permission to release his name or any other personal details. EFE