A salvage operation to recover a Greek registered oil tanker stranded in the Red Sea after an attack by Houthi militants is expected to start in the coming days, two sources with knowledge of the matter said on Friday.

"What was decided yesterday is an initial game plan, of the operation starting in 48 hours," one of the sources said.

A second source said the operation was likely to be complex, since Houthis had rigged the Sounion with explosives.

At stake is the safe removal of a tanker laden with about 1 million barrels of crude that if spilled could cause an environmental catastrophe in an area that is particularly dangerous to access. Efforts are being made to speed up the process, sources said.

A potential oil spill of 2.2 nautical miles (4.1 km) in length has been detected in the area matching the location of the Sounion in the Red Sea, Greece said in a letter circulated through the United Nations' shipping agency on Friday.

"Greece urges all nations and all actors involved to assist in preventing the environmental hazard and resolving the situation the soonest possible," Greece said in the letter dated Aug. 29 and published on Friday.

Yemen's Houthi militants carried out multiple assaults, including planting bombs on the already disabled 900-foot (274.2-meter) Sounion, which is operated by Athens-based Delta Tankers. On Wednesday, the Iran-aligned militants said they would allow salvage crews to tow the ship - which has been on fire since Aug. 23 - to safety.

The sources said the priority of the operation - whether to tow the vessel to a port or arrange a transfer of its cargo - depended on an inspection of the vessel.

"It is not an easy task, transferring the oil cargo to another ship, when there are explosives on it," said one of the sources. "In any case, (EU monitoring mission) ASPIDES ships will protect and escort the vessel to a safe port."

"Delta Tankers is doing everything it can to move the vessel (and cargo). For security reasons, we are not in a position to comment further," a spokesperson for the tanker operator said.

There had been conflicting accounts earlier in the week over whether the Sounion had started leaking its cargo.

The ASPIDES mission said it had not, while the US later clarified initial comments to say some of the spillage was not from the cargo, but from the vessel itself and where it had been hit.

If a spill occurs, it has the potential to be among the largest from a ship in recorded history.

"Houthis have agreed to allow its towing because at the end of the day any environmental disaster would affect their region," said a shipping industry source.