By Michelle Nichols

UNITED NATIONS Oct 20 (Reuters) - A Saudi Arabia-led military campaign in Yemen violated international humanitarian law with a so-called "double tap" air strike on a funeral gathering in the rebel-held capital Sanaa, United Nations sanctions monitors told the Security Council.

The U.N. monitors said there were two air strikes in quick succession on the Oct. 8 funeral, which was attended by many top political and security figures from the Iran-allied Houthi rebels and forces loyal to former President Ali Abdullah Saleh.

In an Oct. 17 report, seen by Reuters, the monitors said they found "in respect of the second air strike, that the Saudi Arabia-led coalition violated its obligations in respect of hors de combat and the wounded in this 'double tap' attack."

Under international humanitarian law, attacks are prohibited against hors de combat - fighters incapable of defending themselves - the wounded, and medical personnel and units.

The Saudi Arabia mission to the United Nations was not immediately available to comment on the U.N. report. An investigative body set up by the coalition said on Saturday that the attack was based incorrect information.

The U.N. has said some 140 people were killed in the attack on the funeral and several hundred more were injured.

"The second air strike, which occurred three to eight minutes after the first air strike, almost certainly resulted in more casualties to the already wounded and the first responders," the U.N. monitors said.

"These first responders included civilians who immediately entered the area after the first air strike to provide urgent first aid and undertake casualty evacuation," the report said.

The monitors recommended that the Security Council consider asking members of the Saudi-led coalition to stop using "double tap" attacks. The coalition includes Kuwait, Bahrain, United Arab Emirates, Qatar, Egypt, Jordan, Morocco, Senegal and Sudan.

The U.N. monitors found that the Saudi-led coalition "did not take effective precautionary measures to minimize harm to civilians, including first responders, in the second strike."

Saudi Foreign Minister Adel al-Jubeir said on Monday that Riyadh was being careful to abide by humanitarian law and that those responsible for the funeral bombing would be punished and the victims would be compensated.

The coalition has been fighting Houthi rebels and forces loyal to Saleh in Yemen since March 2015 to try to restore to power the internationally backed President Abd-Rabbu Mansour Hadi, who has fled into exile.

Saleh and one of his sons reportedly attended the Oct. 8 funeral, but left prior to the air strikes, the U.N. monitors said, signaling that the attack nearly "dealt a devastating political and military blow" to the Houthi-Saleh alliance.

A U.N.-brokered 72-hour truce in Yemen went into effect on Wednesday, but came under pressure on Thursday.

The U.N. sanctions monitors have previously accused the Saudi-led coalition, the Houthi rebels, forces loyal to Saleh and Yemen government troops of violating international humanitarian and human rights law.

(Reporting by Michelle Nichols; Editing by Tom Brown)