The UN has reportedly so far been unable to confirm Iran was involved in drone and cruise missile attacks on two key Saudi oil facilities in September.
Saudi Arabia said Iran was behind the attacks, which temporarily knocked out half of the kingdom's crude production.
But a leaked report by the UN's secretary general says investigators could not corroborate that the drones and missiles were of Iranian origin.
Iran denied any role and noted a claim of responsibility from rebels in Yemen.
The Houthi movement, which is aligned to Iran, said it retaliated for air strikes on Yemen by a Saudi-led coalition backing government forces in the civil war.
What does the UN report say?
UN experts monitoring Security Council sanctions on Iran and Yemen travelled to Saudi Arabia to examine the debris of the drones and missiles.
On Tuesday, Secretary General António Guterres presented a report to the Security Council that summarised the experts' initial findings.
"At this time, [the UN] is unable to independently corroborate that the cruise missiles and unmanned aerial vehicles used in these attacks are of Iranian origin," Mr Guterres wrote in the report, seen by Reuters and AFP news agencies.
But the report also noted that the Houthis "have not shown to be in possession, nor been assessed to be in possession" of the drones used in the attacks.
Mr Guterres said the UN investigation into the attack was continuing and that its results would be submitted to the Security Council when finished.
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