RIYADH: An "oil spot" has been observed in a shipping lane west of a decaying tanker off Yemen's western coast, Saudi Arabia warned the UN Security Council in a letter released Thursday. The 45-year-old Safer, anchored off a Yemeni port since 2015, has 1.1 million barrels of crude on board, and the UN has warned that a rupture or explosion would have catastrophic environmental and humanitarian consequences.

"An oil spot has been observed 50 kilometres (31 miles) west of the vessel inside the transit area of merchant ships," Saudi Arabia's UN Ambassador Abdallah al-Mouallimi wrote in the letter posted on Twitter.

"It is obvious 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."

Yemen's Iran-backed Huthi rebels, who are locked in a five-year conflict with a Saudi-led military coalition, have blocked the United Nations from sending a team of inspectors to assess the vessel.