Britain and Germany condemned on Monday the attacks against Saudi Aramco oil facilities in Abqaiq and Khurais.
British Prime Minister Boris Johnson stands in support of his Saudi Arabian allies following an attack on its oil facilities which marked a "wanton violation of international law", his spokesman said.
German Foreign Minister Heiko Maas slammed the attack, saying "the situation is exceedingly worrisome.”
He added that Berlin is currently evaluating with its partners, "who is responsible for this attack, how it could happen."
Washington has blamed Iran for the attack.
The Tehran-backed Houthi militias in Yemen claimed Saturday's strikes on the plants.
US President Donald Trump said Sunday the United States is "locked and loaded" to respond to the attack.
His accusations were echoed Monday by US Secretary of Energy Rick Perry, who said: “The United States wholeheartedly condemns Iran’s attack on Saudi Arabia and we call on other nations to do the same.”
In an address to the International Atomic Energy Agency's general conference in Vienna, he said "this behavior is unacceptable" and that Iran "must be held responsible."
"Make no mistake about it, this was a deliberate attack on the global economy and the global energy market,” he stressed.
He said Trump has authorized the release of strategic oil reserves should the US need them, and that his "department stands ready" to proceed if necessary.
Perry also added that "despite Iran's malign efforts we are very confident that the market is resilient and will respond."
Tehran and Washington have been at loggerheads since May last year, when Trump pulled the US out of a 2015 deal with world powers that promised Iran relief from sanctions in return for curbs on its nuclear program.