By Jonathan Saul

LONDON, May 19 (Reuters) - A Yemen-bound Iranian aid ship is not being escorted by Iranian warships and is due to arrive in the port of Hodaida on Thursday, two foreign activists onboard the vessel told Reuters on Tuesday.

A coalition of Arab countries led by Saudi Arabia has imposed searches on all ships trying to enter Yemen in a bid to prevent weapons being smuggled to the Iran-allied Houthi group which controls much of the country, including Hodaida.

Saudi Arabia accuses Iran of arming the Houthis - a charge Tehran denies - while Iran has condemned the Saudi-led air strikes against the Houthis. Iranian officials have said they would not let Saudi-led forces inspect the Iran Shahed.

Christoph Horstel, a German political activist on board the vessel, said it was not being escorted. "It is a purely humanitarian mission. There is no ship accompanying us - let alone any Iranian warships," he said.

"As I look at the horizon, there is no ship at all and during the whole trip there was never any warship," said Horstel, who previously worked for Germany's TV ARD.

Caleb Maupin, a native of Ohio who has campaigned against war and the U.S. financial system and is onboard the Iran Shahed, also said he had not seen any escort warship.

Iran's Tasnim news agency on Monday quoted the Iran Shahed's captain as saying two Iranian warships had begun escorting the ship. ID:nL5N0Y92A2

Deputy Chief of Iran's Armed Forces Brigadier General Massoud Jazayeri said last week that any attack on the ship would spark a regional war. ID:nL5N0Y52HL

Horstel said an unidentified plane circled the ship three times on Monday. "It is smooth sailing conditions and the expected time of arrival will be Thursday," he said.

(Editing by Dominic Evans) ((jonathan.saul@thomsonreuters.com; + 44 207 542 4357 ; Reuters Messaging: jonathan.saul.thomsonreuters.com@reuters.net))

Keywords: IRAN SHIP/YEMEN