Houthi rebels have agreed to allow a UN mission to inspect and secure an abandoned oil tanker off Yemen's Red Sea coast, the UN has announced.
The FSO Safer is loaded with more than a million barrels of crude oil and experts have warned of an environmental catastrophe if the vessel breaks apart.
The tanker has had virtually no maintenance since the start of Yemen's devastating civil war five years ago.
UN spokesman Stephane Dujarric said the work could begin early next year.
The rebels reached a deal granting a UN team access to the tanker in July, but the decision was never implemented.
Mr Dujarric said the new agreement, announced in an official letter from the Houthis on Saturday, would be more formal and "represents an important step forward in this critical work".
The 45-year-old FSO Safer is anchored about 60km (37 miles) north of the rebel-held port of Hudaydah, which is a key lifeline for aid supplies to much of Yemen's population.
The UN has repeatedly called for action to avert an oil spill from the rusting vessel, which would not only devastate marine life in the Red Sea, but could also destroy the livelihoods of locals and disrupt aid deliveries.
But securing a more long-term solution has been complicated by a dispute over the oil on board the vessel, which the Houthis have insisted they should be able to sell.
The UN, however, is said to be discussing the division of the proceeds between the Houthis and the Yemeni government, which is backed by a Saudi-led coalition of Arab states.
Yemen's civil war has reportedly killed more than 100,000 people and triggered what the UN says is the world's worst humanitarian crisis.