Calling a recent attack on major Saudi oil facilities "unprecedented," U.S. Defense Secretary Mike Esper says the United States is working with its allies to defend the "international rules-based order that is being undermined by Iran."
Esper made the comments in a tweet on September 16 after the United States issued satellite images and cited intelligence to back its allegation that Iran is behind the September 14 attack on the world's largest oil-processing facility.
Iran denies involvement in the air attack, which was claimed by Iranian-backed Huthi rebels in Yemen.
Unnamed U.S. officials said the direction and extent of the attacks cast doubt on Huthi involvement.
The attack disabled about half of Saudi Arabia's oil production -- the biggest disruption to world crude supplies ever.
"The United States military, with our interagency team, is working with our partners to address this unprecedented attack and defend the international rules-based order that is being undermined by Iran," Esper tweeted after attending a meeting at the White House during which President Donald Trump was briefed on the situation.
Trump later told reporters at the White House that Iran was likely behind the strikes on Saudi Arabia.
"It is certainly looking that way at this moment," he said when asked if he believes Iran carried out the attack.
He added that the United States was not looking at retaliatory options until he has "definitive proof" that Tehran was behind it.
"We'd certainly like to avoid" war, the U.S. president said. "I don't want war with anybody but we're prepared more than anybody."
On September 15, Trump stopped short of directly accusing Iran, but suggested possible military action once the perpetrator was known.
"Saudi Arabia oil supply was attacked," Trump wrote in a tweet. "There is reason to believe that we know the culprit, are locked and loaded depending on verification, but are waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed!"
Iranian Foreign Ministry spokesman Abbas Musavi on September 16 rejected U.S. accusations that Tehran was behind the attack as "unacceptable and entirely baseless."
Speaking after talks with his Russian and Turkish counterparts in Ankara, Iranian President Hassan Rohani called the attack a reciprocal response by "Yemeni people" to "aggression" against their country.
Meanwhile, Russia’s President Vladimir Putin said Saudi Arabia should "make a wise state decision” and buy Russian surface-to-air missiles to protect itself.
The Saudi-led coalition that has been battling the Huthis since March 2015 said the weapons used in the attack were provided by Iran.
"The investigation is continuing and all indications are that weapons used in both attacks came from Iran," coalition spokesman Turki al-Maliki told reporters in Riyadh, adding they were now probing "from where they were fired."
While Washington was quick to point a finger, other countries urged restraint until the picture surrounding the attack, first reported to possibly having been carried out by drones, was clearer.
British Foreign Secretary Dominic Raab called the attack "a wanton violation of international law," but he also said that "in terms of who is responsible, the picture is not entirely clear."
Similarly, China said it was not responsible to accuse others "in the absence of a conclusive investigation or verdict," while Russia warned again "hasty conclusions."
"We aren't positive about the growing tensions in the region and call on all regional and extra-regional countries not to jump to any hasty steps or conclusions that could only worsen the current destabilized situation," Kremlin spokesman Dmitry Peskov told reporters in Moscow.
The weekend attack has rattled world energy markets, sparking the biggest surge in oil prices since 1991.
Trump said he authorized the release of U.S. strategic petroleum reserves "if needed" to stabilize energy markets. The reserve contains about 630 million barrels of oil, according to official data, and past presidents have released quantities during times of crisis, if there are fears of skyrocketing prices.
U.S. Energy Secretary Rick Perry condemned what he called "Iran's attack on the Kingdom of Saudi Arabia" in an address on September 16 in Vienna to the general conference of the International Atomic Energy Agency.
"This behavior is unacceptable and they must be held responsible," Perry said, referring to Iran.
"Make no mistake about it, this was a deliberate attack on the global economy and the global energy market," he added.
By midday of trading on September 16, Brent crude was up 10 percent at $66.33 a barrel, while U.S. light crude was up 9.5 percent at $60.27. Brent crude opened the session up almost 20 percent.
The September 14 attacks reduced production by 5.7 million barrels a day, state oil giant Saudi Aramco said -- nearly half the kingdom's output. That affects 5 percent of the world's daily oil production, Reuters and The Wall Street Journal reported.
Saudi officials said one-third of crude output will be back online on September 16.
Musavi also said that Tehran was ready to take another step in reducing its commitments to the Joint Comprehensive Plan of Action (JCPOA) for Iran's nuclear program, which the United States pulled out of last year.
Iran has already announced three stages of reducing its commitments to the accord in response to sanctions the United States reinstated when Washington abandoned the deal between Iran and world powers including China, Britain, France, Germany, and Russia.
"The third stage [of the process to reduce commitments] continues and preparations are under way for a fourth stage," Musavi said.
The September 15 comments by top Iranian officials followed accusations from U.S. Secretary of State Mike Pompeo, who charged that Tehran had launched "an unprecedented attack" on global energy supplies.
"Tehran is behind nearly 100 attacks on Saudi Arabia while [Iranian President Hassan] Rohani and [Foreign Minister Mohammad Javad] Zarif pretend to engage in diplomacy," Pompeo said in the Twitter post.
Despite the rising tensions, the White House left open the door that Trump could meet with Rohani at the United Nations General Assembly in New York, which begins on September 17.
Musavi, who said earlier that the U.S. accusations were intended to justify "future actions" against Iran, all but ruled out such a meeting, saying "we have neither planned for this meeting, nor do I think such a thing would happen in New York."
A senior Iranian Islamic Revolutionary Guards Corps commander, meanwhile, warned that the country was ready for war.
"Everybody should know that all American bases and their aircraft carriers in a distance of up to 2,000 kilometers around Iran are within the range of our missiles," the semiofficial Tasnim news agency quoted commander Amirali Hajizadeh as saying.
The Huthi rebels are part of a regional network of militant groups aligned with Iran. The Shi'ite insurgent group holds Yemen's capital, Sanaa, and other territory in the Arab world's poorest country.
The conflict has been in military stalemate for years.