Efforts to limit environmental damage from a cargo vessel that sank after a Houthi missile strike and another abandoned during a fiery assault are on hold until attacks on ships ease, the United Nations’ maritime shipping regulatory agency said on Monday.

The UK-owned Rubymar last month became the first vessel lost since the Houthis began targeting commercial ships in the Red Sea area in November. The bulk carrier with 21,000 metric tons of fertiliser contained in its cargo hold has been submerged in shallow waters between Yemen and Eritrea since late February.

The Greek-owned True Confidence was abandoned earlier this month after being set ablaze in an attack that killed three crew members near Yemen’s port of Aden.

Salvage operations, which can include refloating vessels, towing and repairs, are critical to protecting marine life and coastal environments from damage from leaking fuel and hazardous cargo. Damage to the Rubymar caused a 18-mile oil slick and scientists remain concerned that a fertilizer leak could trigger devastating algal blooms in the Red Sea that damage vulnerable coral reefs and harm fish.

“We’re limited in what we can do in an area that is not safe and secure,” Arsenio Dominguez, secretary-general of the UN’s International Maritime Organization (IMO) said at a media briefing in London.

The Houthi’s escalating drone and missile campaign against commercial shipping has choked trade through the vital Suez Canal shortcut between Asia and Europe and forced many ships to take the longer route around Africa.

The Iran-aligned militants say their campaign against commercial vessels in the Red Sea and Gulf of Aden is a show of solidarity with Palestinians against Israel’s offensive in Gaza.

While the IMO is supporting efforts to assist the internationally recognized government of Yemen with salvage efforts in the southern Red Sea, it is difficult to do the same for the True Confidence in the Gulf of Aden, Dominguez said.

“It’s very difficult right now to access the area,” Dominguez said during a meeting of the IMO’s Marine Environment Protection Committee. “Even for us to send consultants to support the Yemeni government for the salvage operations is not possible.”

In the case of the Rubymar, the ship’s fertilizer cargo is “still contained,” Dominguez said. The ship poses safety risks for other vessels navigating the area, he added.

For now, the 18-mile (29 km) oil slick remains the main environmental impact from Rubymar’s sinking, said Dominguez.

A salvage contract for the True Confidence has been signed, a spokesperson for the ship’s companies told Reuters earlier this month, but declined further details, citing security issues.

India’s navy evacuated all 20 crew from the stricken vessel.

The IMO will work with the United Nations Environment Programme and the U.N. Office for the Coordination of Humanitarian Affairs to see how else it can support Yemen, Dominguez said.

A UN salvage team in 2023 avoided what could have been a devastating oil spill off the coast of Yemen by pumping more than 1 million barrels of light crude off the Safer, a decaying super tanker, to another vessel.

The Safer had been used to store oil from Yemen’s oil fields in Marib. It became stranded in the Red Sea in 2015, after the crew abandoned ship due to Yemen’s civil war between the Houthis and a pro-government coalition.