Saudi Arabia and the US have determined "with very high probability" that the attacks on Saudi Aramco facilities was launched from an Iranian base in Iran close to the border with Iraq, a source familiar with the investigation told CNN.
The missiles, according to the investigators' current assessment, flew over southern Iraq and through Kuwaiti airspace before reaching their targets.
The Saudi Defense Ministry said it will hold a news conference on Wednesday to present "material evidence and Iranian weapons proving the Iranian regime's involvement in the terrorist attack.”
But Iran's Defense minister Brigadier General Amir Hatami said Tehran had no involvement in the attacks, Tasnim news agency reported.
Yemen's Houthi militias, who are backed by Iran, have claimed responsibility for the attacks.
Iranian President Hassan Rouhani said the Houthis attacked the Saudi oil facilities as a "warning.”
He said the US accusations that Iran was behind the attacks were aimed at increasing pressure on Tehran.
"While exerting psychological and economic pressure on the Iranian people (through sanctions), they want to impose maximum ... pressure on Iran through slander," Rouhani said according to state broadcaster IRIB. "Meanwhile, no one believes these accusations."