Smoke billows from an Aramco oil facility in Abqaiq about 60 kilometers southwest of Dhahran in Saudi Arabia's Eastern province on September 14, 2019. Photo: AFP

The UN is "unable to independently corroborate" that missiles and drones used in attacks on Saudi oil facilities in September "are of Iranian origin," Secretary-General Antonio Guterres told the Security Council on Tuesday.

The US, European powers and Saudi Arabia have blamed the September 14 attack on Iran. Yemen's Houthi group claimed responsibility for the attacks, and Iran, which supports the Houthis, has denied any involvement.

Guterres said the UN examined debris of weapons used in attacks on a ­Saudi oil facility in Afif in May, on the Abha international airport in June and August and on the Saudi Aramco oil facilities in Khurais and Abqaiq in September.

"At this time, it is unable to independently corroborate that the cruise missiles and unmanned aerial vehicles used in these attacks are of Iranian origin," he wrote in the report, seen by Reuters.

The attacks that targeted the Abqaiq and the Khurais oil plants caused a spike in oil prices, fires and damage and shut down more than 5 percent of global oil supply. Saudi Arabia said on October 3 that it had fully restored oil output.

UN experts monitoring Security Council sanctions on Iran and Yemen traveled to Saudi Arabia days after the September 14 attack.

The report noted that Yemen's Houthis "have not shown to be in possession, nor been assessed to be in possession" of the type of drones used in the attacks on the Aramco facilities.

Guterres reports twice a year to the Security Council on the implementation of an arms embargo on Iran and other restrictions that remained in place after Tehran agreed to a nuclear deal with world powers in 2015.

The council is due to discuss his report next week.

A separate independent panel also reports twice a year to the Security Council on the implementation of sanctions related to the conflict in Yemen that were imposed in 2014 and 2015. That report is due next month.

Saudi Minister of State for Foreign Affairs Adel al-Jubeir told reporters in New York in September that his country had consulted with its allies on what steps to take after the attacks.