UNITED NATIONS — The transfer of more than a million barrels of oil from an aging tanker moored off the coast of Yemen has been completed, preventing an environmental disaster, the United Nations said on Friday.

In a statement, Farhan Haq, the deputy spokesman for UN Secretary-General Antonio Guterres, said the operation had prevented a "monumental environmental and humanitarian catastrophe".

An international team began removing the oil from the dilapidated vessel, known as FSO Safer, on July 25. Almost all the oil is now aboard a replacement tanker, MOST Yemen.

Before the transfer, the Safer, which Yemen used as a floating storage and offloading facility, held four times as much oil as was spilled in the Exxon Valdez disaster off Alaska in 1989, one of the world's worst ecological catastrophes, according to the UN.

International organizations and rights groups warned for years of the potential for a spill or an explosion involving the tanker, which had not been maintained and had damaged pipes and seawater in its engine compartment.

"Today, we can say that the United Nations and a remarkably broad group of partners have succeeded in preventing the worst-case scenario of a catastrophic oil spill in the Red Sea," David Gressly, the UN humanitarian coordinator in Yemen, said.

The dilapidated tanker was moored 6 kilometers from Yemen's western Red Sea ports of Hodeida and Ras Issa, a strategic area controlled by the Iran-backed Houthi rebels who are at war with the internationally recognized Yemeni government.

The transfer marks a major milestone in a plan that needs additional funding to transport the oil away and to move the Safer. The UN said a small amount of oil remains inside the Safer's hull and that the salvage team needs to install a secure system for mooring the replacement tanker in deep water.

"As much of the 1.14 million barrels has been extracted as possible," the UN said. "However, less than 2 percent of the original oil cargo remains mixed with sediment that will be removed during the final cleaning of the Safer."

The tanker, a Japanese-made vessel built in the 1970s, was sold to the Yemeni government during the 1980s to store for export up to 3 million barrels pumped from oil fields in eastern Yemen's Marib Province. The ship is 360 meters long with 34 storage tanks.

Gressly congratulated the company's salvage team for "carrying out the work under very challenging conditions in the Red Sea".

Adam Steiner, chief of the UN Development Program, said that some people had described the Safer tanker as a ticking time bomb.

"I think it is fair to say that as of today, that ticking is no longer an immediate threat," he added.

Xinhua