The US Navy confiscated hundreds of kilograms of heroin from a stateless fishing boat in the Arabian Sea whose crew identified themselves as Iranians, the Fifth Fleet said on Thursday.

"Two US Navy ships seized 385 kilograms (847 pounds) of heroin worth approximately $4 million" from the vessel transiting the Arabian Sea on Monday, said a statement from the US Navy's Fifth Fleet, based in Bahrain.

It added that the confiscated drugs were destroyed at sea by US forces.

"The US Navy released the stateless fishing vessel and its nine crew members, who identified themselves as Iranian nationals, after seizing the drugs," it added.

Two weeks earlier the US Navy said it had rescued five Iranian sailors injured in an explosion on their vessel and seized its cargo of illegal drugs.

US sailors confiscated more than two tonnes of hashish, methamphetamine and heroin from that vessel, which was transiting the Gulf of Oman, the Navy said.

US Navy ships in both cases were operating as part of the international Combined Task Force 150, whose members conduct maritime security and counter-terrorism operations to disrupt illicit activities including the movement of personnel, weapons and narcotics.

"In 2021, CTF 150 has seized illegal drugs worth more than $193 million (at regional wholesale prices) during counter-narcotics operations at sea," Thursday's statement said.

"This is a higher total value than the amount of drugs the task force interdicted in the previous four years combined."