DUBAI (REUTERS) - Iran's navy seized but later released two US surface drones in the Red Sea, accusing the unmanned vessels of jeopardising maritime safety, Iranian state television reported on Friday (Aug 2), in the second such incident in days.

"The (Iranian navy) frigate Jamaran seized the two vessels on Thursday to prevent any possible accident after issuing warnings to the US fleet. After international shipping lanes were secured, the two vessels were released in a safe area," state TV said.

Footage appeared to show more than a dozen Iranian navy personnel pushing two drones into the sea from the deck of their vessel.

On Tuesday, the US Navy said it foiled an attempt by Iran's Revolutionary Guards naval forces to capture an unmanned surface vessel operated by the US 5th Fleet in the Gulf.

Iran said the drone was a danger to maritime traffic.

Iran has been building up its naval presence in the Red Sea, near the coast of Yemen, where Teheran backs the Houthi movement, after sending vessels there more than a decade ago to protect Iranian oil tankers and merchant ships against piracy.

Iran has repeatedly warned the United States about its military activities in the Gulf, saying that the Guards' naval forces have increased patrols to also secure the passage of Iranian ships and combat fuel smuggling.