Saudi Arabia's energy minister has confirmed that drone attacks on its oil facilities knocked out about 50 per cent of the country's production.
Prince Abdulaziz bin Salman bin Abdulaziz told the Saudi Press Agency that explosions at Saudi Aramco's Khurais and Abqaiq plants on Saturday caused several fires that were controlled, but there were no injuries.
He said Aramco will make up for some of the losses with oil stocks.
The attacks have been attributed to Iranian-backed Houthi rebels in Yemen.
The minister said that according to preliminary estimates, 5.7 million barrels a day of oil production were lost, and the supply of ethane and natural gas also was cut by about half.
He said Aramco will provide updated information within 48 hours of restoring full production.
Prince Abdulaziz said the attacks were aimed not only at Saudi Arabia, but also at the world's oil supply and its security.
US secretary of state Mike Pompeo has blamed Iran for the attacks.
In a series of tweets, Pompeo said "there is no evidence the attacks came from Yemen" and pointed the finger at Tehran.
"Iran has now launched an unprecedented attack on the world's energy supply."
The US Energy Department says the US "stands ready to deploy resources from the Strategic Petroleum Oil Reserves if necessary to offset any disruptions to oil markets" in the wake of a drone attack in Saudi Arabia on the world's largest oil processing facility.
In a statement on Saturday night, the department said Energy Secretary Rick Perry has also directed department leadership to work with the International Energy Agency on potential available options for collective global action if needed. Nations of the 30-member IEA seek to respond to disruptions in the oil supply and advocate for energy policy.
The US strategic oil reserves holds 630 million barrels.
The attacks come as US president Donald Trump has held the door open for nuclear talks with Iranian counterpart Hassan Rouhani and as Iran restarted some uranium enrichment in violation of the 2015 nuclear accord.
Pompeo said the US calls on all nations to "condemn Iran's attacks".
"The United States will work with our partners and allies to ensure that energy markets remain well supplied and Iran is held accountable for its aggression," he said.
Australian Associated Press