DUBAI (Reuters) - Operations to salvage 1.1 million barrels of oil from a decaying tanker moored off Yemen's coast will soon begin after a technical support ship arrived on site on Tuesday, the United Nations said.

U.N. officials have been warning for years that the Red Sea and Yemen's coastline was at risk as the Safer tanker could spill four times as much oil as the 1989 Exxon Valdez disaster off Alaska.

The Ndeavor tanker, with a technical team from Boskalis/SMIT, is in place at the Safer tanker off the coast of Yemen's Ras Isa, the U.N. Humanitarian Coordinator in Yemen David Gressley said on Twitter from on board the Ndeavor.

The war in Yemen caused suspension of maintenance operations on the Safer in 2015. The U.N. has warned its structural integrity has significantly deteriorated and it is at risk of exploding.

The U.N. launched a fundraising drive, even starting a crowdfunding campaign, to raise the $129 million needed to remove the oil from the Safer and transfer it to a replacement tanker, the Nautica, which set sail from China in early April.

The salvage operation cannot be paid for by the sale of the oil because it is not clear who owns it, the U.N. has said.

"Work at sea will start very soon. Additional funding is still important to finish the process," the U.N said on its Yemen Twitter account.

Yemen has been mired in conflict since the Iran-aligned Houthi group ousted the government from the capital Sanaa in late 2014. A Saudi Arabia-led military coalition intervened in 2015 aiming to restore the government.

Peace initiatives have seen increased momentum since Riyadh and Tehran in March agreed to restore diplomatic ties severed in 2016.

(Reporting by Nayera Abdallah and Lisa Barrington; Editing by Bill Berkrot)