The US has blamed Iran for a drone attack on the world’s largest oil processing facility and another major oilfield.
Secretary of state Mike Pompeo described the Saturday attack as “unprecedented” and pointed the finger at Tehran despite Yemen’s Houthi rebels claiming responsibility.
He said on Twitter: “Tehran is behind nearly 100 attacks on Saudi Arabia while [Iran’s president and foreign minister] Rouhani and Zarif pretend to engage in diplomacy.
“Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world’s energy supply.”
The Abqaiq facility in Saudi Arabia and the Khurais oil field, operated by the state-owned Saudi Aramco, were hit in the early hours of Saturday, according to the kingdom’s interior ministry.
The strike caused a huge fire at the facility but it is not known if there were any injuries or fatalities.
The attack on the two facilities has affected almost half of Saudi Arabia’s oil output, according to sources speaking to Reuters news agency.
Yemen’s Houthi rebels have said on state TV that they were behind the attacks, with military spokesperson Yahia Sarie threatening more of the same unless the kingdom ends the war.
Mr Sarie said: “The only option for the Saudi government is to stop attacking us.”
The Saudi-led coalition has been fighting the Iran-backed Houthi rebels in Yemen since March 2015 in a war that has killed tens of thousands of Yemenis and pushed the country to the brink of famine.
Saudi Aramco, the state-owned oil giant, has not yet commented.
It describes its Abqaiq oil processing facility in Buqyaq, 205 miles northeast of the capital Riyadh, as “the largest crude oil stabilisation plant in the world” able to produce up to seven million barrels of crude oil a day.
The Khurais oil field is thought to produce over one million barrels of crude oil a day.
There was no initial impact on global oil prices as markets were closed for the weekend.
US president Donald Trump has told Saudi Arabia’s Crown Prince Mohammed bin Salman that the US will support the kingdom’s security and stability, according to the Saudi embassy in Washington.
The crown prince assured Mr Trump that Saudi Arabia is “willing and able to confront and deal with this terrorist aggression”.
UK foreign affairs minister Andrew Murrison said the strike was “totally unacceptable” and that the “Houthis must stop undermining Saudi Arabia’s security by threatening civilian areas and commercial infrastructure”.
The UK foreign office said the UK “condemns the reckless drone attack” and that “threatening civilian areas and commercial infrastructure is dangerous, provocative and completely unacceptable”.
Following the attack, Martin Griffiths, the UN special envoy for Yemen, said he was “extremely concerned” and urged parties to avoid actions that threaten stability in the region.