(Adds activist quote, detail)

DUBAI, May 20 (Reuters) - The captain of an Iranian cargo ship which Iran says is carrying thousands of tonnes of aid to Yemen expects to enter the Bab al-Mandeb strait linking the Gulf of Aden with the Red Sea on Thursday morning, state news agency IRNA reported.

By crossing the strait, the Iran Shahed will sail past Djibouti where the United Nations is co-ordinating aid. U.S. officials have called on Iran to divert the ship to Djibouti to allow the ship's cargo to be inspected.

"If the weather and the ship's technical conditions persist ... we will enter the Bab al-Mandeb strait tomorrow morning," the Iran Shahed's captain Massoud Ghazi Mirsaid was quoted as saying by IRNA on Wednesday.

The ship, carrying aid and foreign activists, is heading to Yemen's western port of Hodaida, where Saudi-led naval forces have imposed inspections on all shipments in a bid to prevent the smuggling of weapons to Iran-allied Houthi rebels.

Tehran, which denies Saudi Arabia's allegations that it is arming the Houthis, has said it will not allow coalition forces to inspect the ship.

German activist Christoph Horstel, who is on board the Iran Shahed, called for the UN or the International Committee of the Red Cross to carry out any inspections.

"Any neutral institution's inspection is highly welcome, since it will prove the Iranian Red Crescent is abiding with regulations to humanitarian aid. War parties' inspections will be clearly rejected," Horstel told Reuters in an email from the ship on Wednesday.

Reuters ship tracking data showed the Iran Shahed positioned south of Aden at 1015 GMT on Wednesday. Horstel said it could arrive at Hodaida on Friday.

(Reporting by Sam Wilkin, additional reporting by Jonathan Saul, editing by Sami Aboudi and Dominic Evans) ((sam.wilkin@thomsonreuters.com; +971 4453 6548; Reuters Messaging: sam.wilkin.thomsonreuters.com@reuters.net))

Keywords: YEMEN SECURITY/IRAN SHIP