The Fifth Fleet, which is based in Bahrain, said the guided-missile cruiser USS Monterey intercepted the vessel and discovered the cargo during a routine boarding, in a two-day operation on May 6-7.

"The cache of weapons included dozens of advanced Russian-made anti-tank guided missiles, thousands of Chinese Type 56 assault rifles, and hundreds of PKM machine guns, sniper rifles and rocket-propelled grenades launchers," it said in a statement.

The arms are in US custody and their source and intended destination is under investigation, it said.

The Fifth Fleet said the Monterey was in operation for 36 hours, providing security for boarding teams.

"After all illicit cargo was removed, the dhow was assessed for seaworthiness, and after questioning, its crew was provided food and water before being released."

The statement did not indicate where the vessel may have come from, but said the US Navy's regular patrols in the region "disrupt the transport of illicit cargo that often funds terrorism and unlawful activity".