The UN warned on Monday that it would cost $20 billion to clean up an oil spill in the event of the “imminent” break-up of an oil tanker abandoned off Yemen.

“Our recent visit to [the FSO Safer] with technical experts indicates that the vessel is imminently going to break up,” the UN humanitarian coordinator for Yemen, David Gressly, said ahead of a conference, hosted by the UN and The Netherlands, to raise funds for an emergency operation to prevent an oil spill.

The 45-year-old FSO Safer, long used as a floating oil storage platform with 1.1 million barrels of crude on board, has been moored off the rebel-held Yemeni port of Hodeida since 2015, without being serviced.

“The impact of a spill will be catastrophic,” Gressly continued at a briefing in Amman. “The effect on the environment would be tremendous... our estimate is that $20 billion would be spent just to clean the oil spill.”

The UN official had earlier announced on Twitter that the Netherlands would host on Wednesday a pledging conference for the international body’s plan to avert the crisis.

Last month, the UN said it was seeking nearly $80 million for its operation. It warned of “a humanitarian and ecological catastrophe centred on a country already decimated by more than seven years of war”.

It said that the emergency part of a two-stage operation would see the toxic cargo pumped from the storage platform to a temporary replacement vessel at a cost of $79.6 million.

Gressly estimated that a total of $144 million would be needed for the full operation, reiterating that $80 million was needed “to secure the oil safely in the initial phase”.

Hundreds of thousands of people have been killed directly or indirectly in Yemen’s seven-year war, while millions have been displaced in what the UN calls the world’s biggest humanitarian crisis.