A rusting tanker containing more than a million barrels of oil has been abandoned off the coast of war-torn Yemen since 2015, threatening a major environmental disaster if it breaks down or explodes.
On Sunday, a UN-owned supertanker arrived to carry out a delicate operation to pump oil from the derelict FSO Safer vessel.
Here are some key facts:

The 47-year-old Safer, which has long been used as a floating platform to store oil, is moored off Yemen’s western port of Hodeidah in the Red Sea, a major shipping route. He did not serve during Yemen’s eight-year civil war.
Located eight kilometers (five miles) off the coast, Safer holds four times the amount of oil that was spilled in the 1989 Exxon Valdez disaster off Alaska.
The systems needed to pump inert gas into its tanks stopped working in 2017, increasing the risk of an explosion. The United Nations and Greenpeace called the ship a “time bomb”.
The budget for the United Nations operation to transport the oil from Safer and tow the ship to the scrap yard is approximately $143 million.
The United Nations says it still needs an additional $22 million to tow the Safer to the recycling yard and safely tie the replacement vessel to ensure safe storage of the oil, until its final destination is determined.

In the event of a spill, the United Nations estimates cleanup costs could reach $20 billion, with potentially catastrophic environmental, humanitarian and economic consequences.
According to the United Nations, a major spill would devastate fishing communities on Yemen’s Red Sea coast, immediately destroying the livelihoods of some 200,000 people.
It could shut down desalination plants on the Red Sea, shutting down the ports of Hodeidah and Saleef – the lifelines for bringing food, fuel and other vital supplies into Yemen, where most of the population depends on aid to survive.
The spill could reach Saudi Arabia, Eritrea, Djibouti and Somalia, and would produce highly polluted air over a large area, exposing entire communities to life-threatening toxins.
The United Nations says maritime traffic through the Bab el-Mandeb Strait to the Suez Canal, the route to the Mediterranean, could be disrupted, costing billions a day.

Attempts to inspect the deteriorating ship have dragged on for years, with the Houthis, who control much of northern Yemen including the port of Hodeidah, refusing UN requests for access.
The Houthis demanded guarantees of delivery of the value of Safer oil to pay the salaries of their employees.
In March last year, the Houthis signed a memorandum of understanding with the United Nations, to establish a framework for cooperation to facilitate the project.
Inspections finally began on May 30, with the arrival of a team of experts from the private company SMIT Salvage who began preparations for the operation.
In June, the United Nations secured insurance coverage for the complex and risky operation, clearing up another major hurdle.

Earlier this month, the United Nations said SMIT had declared the ship stable enough to transfer from ship to ship.
The Nautica, a supertanker bought by the United Nations to transport oil, arrived from Djibouti on Sunday and was scheduled to dock alongside the Safer. The pumping process is expected to start within three days.
Peter Berdovsky, CEO of SMIT Salvage’s parent company Boskalis, said last month that removing the oil could take between a week and a month, depending on how easily it was pumped.
However, even after transportation, the decomposing Safer will still “present a residual environmental threat, as it retains viscous oil residue and remains at risk of collapse,” the UN warned.
During and after the transfer, SMIT will assess how much oil sludge remains in the Safer tanks, and it will be transferred to a designated yard for cleaning, or if it is too fragile to move, cleaned on site.
The Safer is meant to be completely shut down, with its parts recycled. The Nautica will be renamed Yemen, and will remain in the region as talks continue over who controls the ship and the oil.