A partial view of Saudi Arabia's Abqaiq oil processing plant on September 20, 2019. - Saudi Arabia said on September 17 its oil output will return to normal by the end of September, seeking to soothe rattled energy markets after attacks on two instillations that slashed its production by half. (AFP)

The UN has been unable to confirm Iranian involvement in a dramatic attack on oil facilities in Saudi Arabia earlier this year, secretary-general Antonio Guterres said Tuesday.

Drones and cruise missiles were used in the September bombardment, which knocked out half of the kingdom’s crude production and fueled a record surge in prices.

Saudi officials, the United States and several European countries accused Iran of responsibility for the attack, which Tehran has denied.

UN investigators had been given access to debris of the weapons used in the attack, Guterres said in a six-monthly report to the Security Council on Iran’s nuclear program, seen by AFP on Tuesday.

But the investigation was not able to “independently corroborate that the cruise missiles and unmanned aerial vehicles used in these attacks are of Iranian origin,” the report said.

An investigation into the attack is continuing and will be submitted to the Security Council when finished, Guterres said.