President Donald Trump said in a tweet on Sunday that America was "locked and loaded" in response to attacks on two of Saudi Arabia's oil facilities.

The Saturday attacks shut down production on roughly 5% of the world's daily production of crude oil, equal to about 5 million barrels.

Yemen's Houthi rebel group has claimed responsibility for the attacks, but US officials have cast doubt on that narrative and have pointed a finger toward Iran.

Secretary of State Mike Pompeo said in a tweet Saturday that Iran launched "an unprecedented attack on the world's energy supply."

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President Donald Trump on Sunday evening said America was "locked and loaded" in response to attacks on two Saudi oil facilities that wiped out nearly half of Saudi Arabia's oil production.

Trump in a tweet said his administration had "reason to believe that we know the culprit" and hinted that the US was prepared to act upon "verification" of its suspicions.

Trump's statements followed comments from earlier by Secretary of State Mike Pompeo pinning the blame on Iran for the Saturday attacks, which shut down production on roughly 5% of the world's daily production of crude oil, equal to about 5 million barrels.

"Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply," Pompeo said in a tweet on Saturday.

Yemen's Houthi rebel group claimed responsibility for the attacks, saying it used drones to set the two major oil facilities ablaze. But Saudi and US officials have cast doubt on that narrative, arguing that evidence suggested the attack was launched from Iran.

A senior US official told media, including Reuters, that evidence indicated the attacks were launched from west or northwest of the facilities, the direction of Iran. The official added that Saudi officials had suggested those responsible might have used cruise missiles to launch the attack.

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"There is no evidence the attacks came from Yemen," Pompeo said in his tweet. He also called on global leaders to "publicly and unequivocally 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 wrote in a follow-up tweet.

Iran says it's prepared for a 'full-fledged war'

Members of the Iranian Revolutionary Guard marching in a parade in 2011 to commemorate the anniversary of the Iran-Iraq war. REUTERS/Stringer/File Photo

Tehran has denied allegations that it orchestrated the attack. An Iranian Foreign Ministry spokesman, Abbas Mousavi, said on Sunday that Pompeo's statements were "obscure and meaningless" for diplomatic progress, the semiofficial Tasnim news agency reported.

The agency also quoted a senior Iranian Revolutionary Guard commander as saying the country was prepared for a "full-fledged war."

"Everybody should know that all American bases and their vessels in a distance of up to 2,000 kilometers (from Iran borders) are within the range of our missiles," Gen. Amir Ali Hajizadeh said on Saturday.

Oil prices on Monday skyrocketed to their highest levels in six months, according to Reuters, while US crude futures climbed 15%.

The White House adviser Kellyanne Conway did not rule out a meeting between Trump and Iranian President Hassan Rouhani but told "Fox News Sunday" that recent attacks "did not help" prospects. She added that the administration was keeping "many options on the table" in terms of retaliation.

"This president and his national security team keep many options on the table particularly when it comes to retaliating against malign behavior," she said.

Trump on Sunday night tweeted that news suggesting that he would be willing to meet with Iran with "no conditions" was "fake news."