WASHINGTON, June 28 (Reuters) -

Drone attacks on Saudi Arabia's oil industry in May originated in Iraq, not Yemen, U.S. officials have concluded, drawing questions from Iraqi officials who have asked Washington for more information supporting the claim, the Wall Street Journal reported on Friday.

U.S. officials familiar with the intelligence on the May drone attacks say they originated in southern Iraq, the Journal reported, saying that most likely pointed a finger at Iran-backed militias in that region.

Yemen's Iran-backed Houthis, who have been battling a Saudi-led military coalition for four years, said they carried out the drone strikes against the East-West pipeline.

The drone attack happened two days after four vessels, including two Saudi oil tankers, were damaged by sabotage off the coast of the United Arab Emirates.

The attacks took place against a backdrop of U.S.-Iranian tension following Washington’s move last month to try to cut Tehran's oil exports to zero and beef up its military presence in the Gulf in response to what it called Iranian threats.

The State Department declined to comment on the report.

At a weekly news conference on Tuesday, Iraqi Prime Minister Adel Abdul Mahdi denied the attacks could have come from Iraqi territory.

"All of our intelligence services and our air force denied these reports because the air space is known," Mahdi said. "As far as we are concerned, we have no proof and we have no evidence in this matter."