Washington has now forcibly halted six ships it said were attempting to violate the blockade, which has been in place since April 13.

The Botswana-flagged M/T Lexie -- an unladen oil tanker -- "ignored repeated warnings" over a 24-hour period, and an American warplane "ultimately disabled the vessel by firing a Hellfire missile into the ship's engine room," the US military's Central Command (CENTCOM) said in a statement.

The statement did not mention if the attack caused any casualties aboard the Lexie.

On Friday, the US military similarly disabled a Gambia-flagged cargo vessel after it too failed to comply, CENTCOM said.

On May 8, US forces fired munitions down the smokestacks of two Iranian-flagged tankers to halt them, while a warplane disabled another Iranian-flagged ship on May 6 by firing its 20mm cannon at the vessel's rudder.

And on April 19, an Iranian-flagged vessel attempted to violate the blockade and ignored multiple warnings from a US destroyer, CENTCOM said at the time.

The American warship eventually directed the ship's crew to evacuate its engine room, which it then hit with multiple rounds from its five-inch gun.

Tehran's forces effectively closed the vital Strait of Hormuz waterway -- a key route for oil and gas shipments -- after the start of the US-Israeli war against Iran on February 28.

The United States announced its blockade of Iranian ports after peace talks in Pakistan failed to achieve a breakthrough in April.