(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.

Read More