LONDON/ADEN (Reuters) - An explosion has damaged a Turkish vessel carrying wheat to Yemen’s Houthi-controlled port of Saleef, with varying accounts attributing the incident on Thursday to an unexplained blast aboard the ship or a possible missile strike.

A naval ship of a Saudi-led military coalition received a call from the captain of the vessel, the Ince Inebolu, who reported an opening had appeared in the middle of the ship on the left side, a spokesman for the alliance said.

“Coalition forces conducted a survey of the incident and visited the ship and found an explosion from the inside to the outside,” the spokesman said in a statement.

The captain said he did not know the cause of the damage, the spokesman said. The coalition later towed the ship to the port of Jizan in Saudi Arabia.

A shipping source said separately it was possible the damage was either caused by overheating of parts of the ship or a missile.

A separate source connected with the shipment said the vessel was carrying 50,000 tons of Russian milling wheat, adding that it was unclear if it was hit by a missile or due to an internal blast, while anchored about 70 miles off Saleef, which is just north of the port of Hodeidah on the Red Sea.

The ship was in a waiting area, the source said, where vessels typically anchor for permission to dock.

Reuters was unable to independently confirm whether a missile was fired.

The vessel’s Istanbul based owner Ince Shipping Group did not immediately respond to a request for comment.

Ship tracking data on Reuters showed the Turkish flagged Ince Inebolu bulk carrier’s last position as of 1157 GMT on Friday as being underway in the Red Sea with Saleef as its destination.

Commercial vessels off the coast of Yemen have come under periodic missile attack by the armed Houthi movement during Yemen’s three-year-old war.

The coalition has carried out thousands of air strikes against the Houthis since 2015 to restore the internationally recognized government. At least 10,000 people have been killed and three million forced to flee their homes.

Saleef port workers said the matter has been referred to U.N. Verification and Inspection Mechanism), an entity set up in 2016 to ease delivery of commercial goods through the blockade.

UNVIM did not immediately respond to a request for comment.