Action is being taken to prevent about a million barrels of oil from leaking into the Red Sea from a tanker attacked by Houthi rebels.

The Greek-owned and -flagged MV Sounion was abandoned by its crew off the coast of Oman following an August 21 attack by a Yemeni rebel group.

Private companies, under the protection of the European Union military, will attempt to save the ship, which has the potential to cause one of the world’s largest oil spills from a tanker and was still burning on Monday.

The Houthis have attacked several ships in the Red Sea in the past 10 months, in what the Iranian-backed group says are actions aimed at supporting Hamas in the Gaza Strip.

The US military said on Tuesday evening that the damaged tanker “risks the possibility of a major ecological catastrophe” and accused the Houthis of “irresponsible acts of terrorism”.

A rescue operation was reported to be “underway,” although it was unclear whether rescue ships had yet reached Sounion.

On Monday, EU military operations in the region said several fires were still burning on the tanker’s main deck, although there were no visible signs of an oil leak.

The Houthis – who falsely claimed they were only targeting Israeli, American and British ships – attacked the Sounion with gunfire before hitting it with three unidentified missiles, the UK Maritime Trade Operations (UKMTO) said last week. Twenty-five crew members were rescued by a European warship.

The tanker was later attacked again. The group released a video showing Houthi fighters boarding the ship and setting fire to its deck.

The Houthi leader called the attack “brave and bold” in a recent speech.

The U.S. State Department has previously warned that the Sounion spill could be almost four times larger than the one caused by the 1989 Exxon Valdez tanker disaster, in which 2,100 km (1,300 miles) of coastline was contaminated when the tanker ran aground off the coast of Alaska.

The Houthis have continued to attack oil tankers in the Red Sea in recent days.

On Monday, the U.S. military said two oil ships were hit by ballistic missiles and a drone, including the Saudi-owned, Saudi-flagged MV Amjad, which was carrying about two million barrels of crude.

The U.S.-led military operation carried out the attacks in Yemen, where the Houthis control most of the country, aiming to make it harder to attack ships passing through one of the world’s busiest shipping lanes.