US Secretary of State Mike Pompeo  (Photo: Xinhua)

US Secretary of State Mike Pompeo headed to the United Arab Emirates Thursday for further talks with Gulf allies about responding to major attacks on Saudi oil infrastructure which he has denounced as an "act of war" by Iran.

The hardening of the US position raises the risk of a dangerous escalation in the tinderbox region after weekend strikes on the heart of the Saudi oil industry knocked out half its production

Pompeo flew to Abu Dhabi from the Saudi city of Jeddah, where he met late Wednesday with Crown Prince Mohammed bin Salman, the kingdom's de facto ruler who has said the assault poses a "real test" of global will.

The two sides "agreed that the Iranian regime must be held accountable for its continued aggressive, reckless, and threatening behavior," US State Department spokeswoman Morgan Ortagus said in statement after their talks.

The "unacceptable and unprecedented attack... not only threatened Saudi Arabian national security, but also endangered the lives of all the American citizens living and working in Saudi Arabia," she added.

Pompeo denounced the unprecedented strikes as an Iranian "act of war", as Riyadh Wednesday unveiled new evidence it said showed the assault was "unquestionably" sponsored by Tehran.

Saudi officials displayed what they said were fragments of 25 drones and cruise missiles fired on Saturday at two facilities in the country's east, engulfing them in flames.

"The attack was launched from the north and unquestionably sponsored by Iran," Saudi Defence Ministry spokesman Turki al-Maliki said, but would not be drawn on whether Saudi officials believed Iran would ultimately be found to be the culprit.

Tehran-linked Huthi rebels in the kingdom's southern neighbour Yemen have claimed responsibility, but both Washington and Riyadh have ruled that out, saying it was beyond their capabilities.

French Foreign Minister Jean-Yves Le Drian also said Thursday that the Huthi claim "lacks credibility".

The Huthis have hit dozens of targets in Saudi Arabia, and their rapidly advancing arsenal has exposed the vulnerability of the kingdom despite its vast military spending.

Huthi military spokesman Brigadier Yahya Saree said however that the assault on the two facilities was launched from three locations inside Yemen, using advanced drones with long-range capabilities.