The 19-day operation will pump more than one million barrels out of the rusting vessel, the Safer, which was abandoned over eight years ago, to a nearby replacement vessel.

Secretary-General António Guterres said the UN has taken on the delicate operation as a spill would spell environmental catastrophe for the region.

‘Ticking time bomb’

“United Nations has begun an operation to defuse what might be the world’s largest ticking time bomb. This is an all-hands-on-deck mission and the culmination of nearly two years of political groundwork, fundraising and project development" said the UN chief.

Lying north of the Yemeni port Hudaydah, UN officials have warned for years about the possibility that the 47-year-old tanker could crack and explode.

The supertanker holds four times the amount of oil spilled by the Exxon Valdez – enough to make it the fifth largest oil spill from a tanker in history.

Existential marine threat

UNDP warned that a massive spill from the Safer would destroy swathes of marine life in the Red Sea. Speaking to reporters in Geneva, spokesperson Sarah Bel expressed concern for the fishing communities on Yemen’s Red Coast, already living in a crisis-wracked situation, as a spill would like ‘wipe out 200,000 livelihoods instantly” and "fish stock would take twenty five years to recover.”

Describing the operation as the first of its kind, she exercised caution during this “emergency phase” but assured reporters that everything had been put in place to “secure success.”

The FSO Safer has been moored some 4.8 nautical miles southwest of the Ras Issa peninsula on Yemen’s west coast for more than 30 years. In 2015, production and the maintenance of the tanker stopped due to the eight year conflict between a pro-Government Saudi-led coalition, and Houthi rebels. As a result, the vessel is now beyond repair.

Humanitarian and environmental disaster

According to UNDP, an oil spill would result in the closure of all ports in the area, cutting off food, fuel and other life-saving supplies to Yemen - a country where 80% of the population already rely on aid.

The UN chief warned that the cost of a cleanup alone would be $20 billion and said that shipping all the way to the Suez Canal could be disrupted for weeks.

Praising the project’s cross-UN collaboration he highlighted the "relentless political work” that the operation entailed “in a country devastated by eight years of war.” But noted that this was just a “milestone in the journey”, as the next step involves securing the replacement vessel to a specialised safety buoy.

The UN Secretary-General has called for a further $20 million to finish the project, including the scrapping of the Safer and removing any remaining environmental threats to the Red Sea.