The UN said Yemen's Houthi rebels are delaying a mission to repair an abandoned, decaying tanker, which could spill more than a million barrels of oil into the Red Sea off the country's coast.
UN spokesman Stephane Dujarric said the Iran-backed Houthis had not provided written security guarantees for repair teams, delaying work scheduled to take place this week and raising costs by “hundreds of thousands of dollars”.
The group asked the UN to pause planning for the mission as officials consider a review of their approval for the repairs, which was granted late last year, Mr Dujarric said on Tuesday.
“In light of these challenges, the timeline of the mission remains uncertain and dependent on the continued facilitation of all stakeholders involved.
"We hope to receive a renewed commitment from the Houthi authorities to resolve this urgent matter as soon as possible. Any other outcome would be extremely disappointing."
He said the UN had already spent $3.35 million hiring engineers and leasing ships and gear to repair the FSO Safer tanker, which is moored off the Ras Issa oil terminal, 60 kilometres north of the Houthi-held port of Hodeidah.
The UN said that the 45-year-old vessel, stranded since 2015, could spill four times as much oil as the 1989 Exxon Valdez disaster near Alaska, but access to it has been complicated by the Houthis.
The rebels previously allowed UN teams to board the vessel only to later change their minds.
Divers managed to plug a leak in the ship’s engine room last May but experts say the tanker could fall apart at any minute.
"The UN remains committed to doing everything possible to address the grave humanitarian and environmental threat posed by the Safer tanker, which is carrying 1.1 million barrels of oil and is at risk of rupture," Mr Dujarric said.
UN work in Yemen is further complicated by a US decision in the final days of the Trump administration, which classified the Houthis as terrorists.
That effectively forced some humanitarian groups and importers to stop work there for fear of US sanctions, the UN said.
The Biden administration is reviewing that classification.
Yemen has been riven by conflict since the Houthis drove the government from the capital Sanaa in 2014.
A Saudi Arabia-led military coalition in 2015 intervened in a bid to restore the government.