NEW YORK (Reuters) - Saudi Arabia warned the U.N. Security Council on Wednesday that an “oil spot” had been seen in a shipping transit area 31 miles (50 km) west of a decaying tanker that is threatening to spill 1.1 million barrels of crude oil off the coast of Yemen. The Safer tanker has been stranded off Yemen’s Red Sea oil terminal of Ras Issa for more than five years. The United Nations has warned that the Safer could spill four times as much oil as the 1989 Exxon Valdez disaster off Alaska.In a letter to the 15-member body, reviewed by Reuters, Saudi Arabia’s U.N. Ambassador Abdallah Al-Mouallimi wrote that experts had observed that “a pipeline attached to the vessel is suspected to have been separated from the stabilizers holding it to the bottom and is now floating on the surface of the sea.” The United Nations has been waiting for formal authorization from Yemen’s Houthi movement to send a mission to the Safer tanker to conduct a technical assessment and whatever initial repairs might be feasible.The Security Council and U.N. Secretary-General Antonio Guterres have both called on the Houthis to grant access. Al-Mouallimi wrote that the tanker “has reached a critical state of degradation, and that the situation is a serious threat to all Red Sea countries, particularly Yemen and Saudi Arabia,” adding “this dangerous situation must not be left unaddressed.” Yemen has been mired in conflict since the Iran-allied Houthi group ousted the government from the capital Sanaa in 2014. A Saudi-led military coalition in 2015 intervened in a bid to restore the government. Reporting by Michelle Nichols; editing by Richard Pullin