The United States compelled Iran for a second time this week to release U.S. military sail drones that it tried to seize at sea, U.S. officials said on Friday.
Iran has been building up its naval presence in the Red Sea, near the coast of Yemen where Tehran backs the Houthi movement.
The incident there, after an earlier one in the Gulf, was the latest reminder of U.S.-Iran military tensions, even as both countries pursue nuclear talks. They follow exchanges of fire last week between U.S. troops and Iran-backed groups in Syria.
Iran state television earlier on Friday acknowledged the Iranian Navy released two U.S. maritime drones in the Red Sea but accused the American unmanned vessels of jeopardizing maritime safety, without providing evidence.
"The (Iranian navy) frigate Jamaran seized the two vessels on Thursday to prevent any possible accident after issuing warnings to the U.S. fleet. After international shipping lanes were secured, the two vessels were released in a safe area," the TV said.
The U.S. Navy, in a statement, challenged that account, saying the drones were in an assigned patrol area at least four nautical miles from the nearest maritime traffic lane.
"The vessels posed no risk to naval traffic and had been operating in the general vicinity of the Southern Red Sea for more than 200 consecutive days without incident," the Navy statement said.
A U.S. defense official, speaking on condition of anonymity, suggested the Iranians sought to secretly seize the drones, pulling the sail drones completely out of the water on Thursday and then covering them with tarps.
Iran initially denied having any U.S. property before returning them on Friday to the U.S. warships that converged on the scene, a U.S. official said.
Iranian television footage aired on Friday appeared to show more than a dozen Iranian navy personnel pushing two drones into the sea from the deck of their vessel.
The Navy statement said the U.S. Navy guided-missile destroyers USS Nitze and USS Delbert D. Black stayed near the Iranian warship, communicating with it "to deescalate the situation and recover the seized Saildrones."
The Iranian warship released the drones in the morning on Sept. 2, the U.S. Navy said.
On Tuesday, the U.S. Navy said it foiled an attempt by Iran's Revolutionary Guards naval forces to capture an unmanned surface vessel operated by the U.S. 5th Fleet in the Gulf. Iran said the drone was a danger to maritime traffic.
Iran has repeatedly warned the United States about its military activities in the Gulf, saying that the Guards' naval forces have increased patrols to secure the passage of Iranian ships and combat fuel smuggling.
The U.S. military, meanwhile, has expanded its use of sea-based drones in the region.
It is unclear if Iran might be seizing the U.S. drones in an attempt to copy them. Some of Iran's drones are based on unmanned aircraft from other countries, and it tried to copy an aerial U.S. RQ-170 Sentinel reconnaissance drone captured in 2011.
Iran and the regional forces it backs have increasingly relied in recent years on drones in Yemen, Syria and Iraq. U.S. officials say Iran is supplying drones to Russia for use in the war in Ukraine, which Tehran has denied.
(Reporting by Phil Stewart in Washington and Dubai newsroom;Editing by Andrew Cawthorne, Philippa Fletcher and Richard Chang)
