(CNN) - An abandoned tanker loaded with oil is threatening a major environmental disaster near the coast of Yemen, the United Nations has said, amid expert warnings of a "catastrophic" explosion.
The decaying SAFER FSO tanker contains an estimated 1.1 million barrels of oil and has been moored and left without maintenance near the Yemeni port of Ras Isa for several years, according to the UN.
Mark Lowcock, the UN undersecretary-general for humanitarian affairs, told the UN Security Council last week that the agency was planning to deploy an assessment team to the tanker this week, but was not able to secure the necessary permits.
He said the Houthi authorities that control the region "continue to delay" the assessment, despite the fact that they themselves asked the UN for assistance early last year.
The tanker has been stranded since 2015 and could be extremely dangerous.
"Because the engines haven't been running, the inert gases that are pumped into the storage tanks to stop the build-up of explosive gases from the stored oil haven't been topped up, which is why there are worries about a catastrophic explosion," Doug Weir, research and policy director at the UK-based Conflict and Environment Observatory, told CNN.
The aging tanker had been converted into a floating storage platform before the war in Yemen started.
It would normally transfer Yemeni oil from the Ras Isa port into other tankers for shipment. However, the military conflict between the Houthi rebels and the government backed by the Saudi-led coalition has put a stop to oil trade in the country, shuttering its pipelines and ports.
The cargo that is stuck on board the ship could be worth more than $60 million, based on current oil prices.
According to the Houthi-run Al-Masirah news agency, the Houthi government has previously demanded safeguards from the UN that it would be able to sell any oil extracted from the vessel, something that is currently impossible because of international sanctions.
Lowcock has said that depending on the time of year and water currents, a spill from the tanker could reach from Bab el Mandeb to the Suez Canal -- and potentially as far as the Strait of Hormuz.
"I leave it to you to imagine the effect of such a disaster on the environment, shipping lanes and the global economy," he said in a speech to the Security Council.