The Yemeni government says it will hold Houthi rebels responsible for any environmental disaster if an abandoned tanker holding over a million litres of oil sinks after water flooded through cracks in the ageing hull.

The FSO Safer oil tanker, moored off Yemen’s western coast since 2015, is rusting away with nearly 1.1 million barrels of oil on board. The UN has tried to send a team to assess the risk amid international calls for action but so far efforts to unload the oil and make the rusting hulk safe have been hampered by the Iran-backed Houthi rebels.

“New photos show leakage of water spilling on to the tanker. There is a possibility of it sinking or exploding at any moment, which has an impact over the environment which will affect Yemen and other states around the Red Sea,” Yemen’s Infomation Minister Muammar El Eryani said on Twitter.

The images showed water pouring through cracks although the Conflict and Environment Observatory said the images of the tanker were actually from an engine room leak in May.

"Which is not to downplay the urgency of action to salvage the FSO Safer, on the contrary, it grows more urgent by the day," the observatory said on Twitter.

The leak sparked an emergency UN meeting and a warning that a full spillage would be four times larger than the Exxon Valdez disaster off Alaska in 1989.

If a disaster occurs, the government will hold the Iran-backed Houthi rebels responsible, he said.

“Especially after brushing off international calls, warnings and not following up on their commitments to allow a team of UN experts to inspect the ship,” Mr Al Eryani added.

Last month, the Houthis said a team of UN engineers would be allowed to visit the ship but reports in recent days suggest the rebels have blocked them from boarding.

The government agreed, without any conditions, for a UN team to arrive and inspect the tanker, but the visit has yet to take place.

The tanker was used as a bulk storage to export the country's small crude oil resources but has lain unsecured for years.

The government said the tanker must be disposed of immediately and warned of an environmental catastrophe if the vessel breaks apart and the oil is leaked into the sea.

"The international community, the UN and Security Council urged the Houthis to immediately contain the risks of explosion or sinking of the tanker and to not turn it into a bargaining chip," Mr El Eryani said.

They must pressure the rebels "to allow a technical team to assess the status of the tanker and to begin immediate maintenance work," he said.

The tanker has had almost no maintenance since the conflict in Yemen intensified five years ago.

If the oil spills, it will have devastating consequences for the Arab world’s poorest country, which is already dealing with a civil war and a severe humanitarian crisis.