Saudi oil attacks an 'act of war', says Pompeo

US Secretary of State Mike Pompeo denounced strikes on Saudi Arabia's oil infrastructure as an "act of war" Wednesday, as Riyadh unveiled new evidence it said showed the assault was "unquestionably" sponsored by arch-foe Iran.

The comments raise the risk of a wider conflict in the tinderbox Gulf region after the weekend strikes on the heart of the kingdom's oil industry knocked out half its production.

"This was an Iranian attack," Pompeo told reporters on his plane before landing in the western city of Jeddah, calling it "an act of war".

His comment came as Saudi Arabia displayed what it said were fragments of 25 drones and cruise missiles fired at two facilities in the country's east, leaving them engulfed in flames.

"The attack was launched from the north and unquestionably sponsored by Iran," defence ministry spokesman Turki al-Maliki said.

"We are working to know the exact launch point."