The Pentagon said an oil tanker attacked by Yemen’s Houthi rebels in the Red Sea last week is still on fire and may be leaking oil.
The defence ministry added that attempts to salvage the Greek-flagged MV Sounion had been blocked by the Houthis, who have threatened further attacks.
The ship is carrying more than 150,000 tonnes (1 million barrels) of crude oil, and a major spill could make it the largest ship-related oil spill in history.
The Iran-backed Houthis, who control much of Yemen, say they have been attacking shipping in the Red Sea for 10 months to support the Palestinians in their war against Israel and Hamas in the Gaza Strip.
During that time, they reportedly sank two ships and killed at least two crew members.
They have claimed, often falsely, that they only target ships linked to Israel, the US and the UK.
The UK Maritime Trade Office (UKMTO) said the Sounion was first shelled by two small boats last Wednesday, then hit by three unidentified projectiles, causing a fire and disabling its engines.
The 25 crew members were rescued by a European warship the following day and taken to Djibouti.
The oil tanker then came under attack again, with the Houthis posting a video that appeared to show them setting the tanker on fire.
The US State Department expressed concern about the attack on the Sounion in a statement on Saturday, warning that it could result in an oil spill four times larger than the 1989 Exxon Valdez oil spill, which released 257,000 barrels of oil off the coast of Alaska.
Pentagon spokesman Maj. Gen. Patrick Ryder said Tuesday that two tugboats had been sent to try to free the distressed vessel, but that the Houthis had threatened to attack the tugboats as well.
He said the United States was working with regional partners to mitigate potential environmental impacts.
