The UN Security Council will meet this week to discuss a long-abandoned fuel tanker off Yemen amid growing fears of a catastrophic oil spill, diplomats said Wednesday.

Thursday's meeting, requested by Britain, comes after Huthi rebels said an agreement to allow a UN mission to inspect the tanker had "reached a dead end."

The 45-year-old fuel vessel FSO Safer has 1.1 million barrels of crude on board and has been abandoned near Yemen's western port of Hodeida since 2015.

UN inspectors were initially meant to assess the tanker last year but the mission has been repeatedly delayed over disagreements with the rebels.

A spokesperson for Britain at the UN said there was a "grave risk" of an oil spill "which would be catastrophic for Yemen and the region."

"The responsibility for the tanker lies with the Huthis and they must cooperate with the UN. We are bringing this issue to the UN Security Council tomorrow to discuss next steps," he added.

The Huthi rebels said Tuesday that negotiations with the UN had reached an impasse after several days of talks, according to their Al-Masira channel.

They said they "deeply regret the UN's backing out of conducting maintenance work (in a deal) that was signed last November."

Stephane Dujarric, spokesman for UN Secretary General Antonio Guterres, reiterated that maintenance work can't be undertaken without an impartial assessment first.

He said the rebels' comments "seem to confirm that the Huthis aren't ready to provide the assurances we need to deploy the UN mission to the Safer."

"The Safer is a dangerous site, and we need to understand exactly what we're dealing with before undertaking any major works," Dujarric said.

The UN has said an oil spill would destroy Red Sea ecosystems, shut down the fishing industry and close Yemen's lifeline Hodeida port for six months.

Apart from corrosion to the ageing vessel, essential work to curb explosive gases in its storage tanks has been neglected.