"I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!" Trump tweeted.
He did not specify what those sanctions would be.
Trump's announcement came as a Saudi military spokesman said the strikes on its oil sites were "unquestionably sponsored by Iran."
The Trump administration is considering a variety of responses, both economic and military, to last weekend's attack on a Saudi oil production. Trump administration officials have also said Iran was behind the drone and missile strikes, which temporarily slashed Saudi Arabia's oil producing capacity.
Iranian officials have denied any role in the attack and accused the United States of warmongering. The Houthis, an Iranian-backed rebel group engaged in a brutal war with Saudi Arabia, has claimed responsibility for the strikes.
Secretary of State Mike Pompeo is scheduled to be in Saudi Arabia on Wednesday to speak with the kingdom's leaders about potential responses to the oil facility attack.
Saturday's strikes hit the Abqaiq oil processing plant and a key Saudi oil field, where an estimated 5.7 million barrels of oil are produced each day. The attacks, which disrupted more than 5% of the world's daily supply, have renewed fears of a military confrontation between the U.S. and Iran.
A senior administration official, who briefed reporters Tuesday on the condition of anonymity, said the Houthis could not have carried out such a sophisticated operation.
Trump and aides have said they are considering a variety of aggressive actions toward Iran, ranging from more cyber attacks to a strike against Iranian oil facilities.
The Pentagon is planning military responses to the Sept. 14 attack on oil facilities in Saudi Arabia, Marine Gen. Joe Dunford, chairman of the Joint Chiefs of Staff, told reporters on Tuesday.
But Dunford stressed that economic, diplomatic and political options are also under consideration. Iran or its proxies are likely behind the attacks, he said.
"In the region, wherever it originated from, the most likely threat is either Iran or Iranian-backed proxies," Dunford said. "Without getting out in front of the Saudi investigation, I think that is a reasonable conclusion."
Central Command, which oversees U.S. military operations in the Middle East, has sent a team to Saudi Arabia to sift through traces of the weapons used to determine their origin. The Saudis have not requested additional military resources.
Dunford noted that Iranian-backed proxies have struck Saudi Arabia several times, but the Sept. 14 attack was the largest. Iran has supported Houthi rebels who are fighting Saudi-supported forces in Yemen.
"Without prejudging intelligence, this looked like a very complex, precise attack, not consistent with previous Houthi attacks," Dunford said.
Sen. Lindsey Graham, a defense hawk and normally a staunch Trump ally, said he thinks new sanctions will not be enough to deter Iran from future attacks.
“I am looking for a response that would be unequivocal. If they don’t pay a price for bombing a neighbor’s oil fields, then all hell is going to break out in the Mideast,” Graham told reporters Wednesday on Capitol Hill.
He said the U.S. should build support for a multilateral response.
“I am not looking for a response immediately,” he said. "But I am looking for a response that would restore deterrence, and my belief is that additional sanctions will fall short.”
The Trump administration has already slapped Iran with crippling sanctions, aimed at driving the country’s oil exports to zero and choking Tehran’s economy.
The goal, administration officials say, is to force Iran back to the negotiating table after Trump withdrew from the 2015 nuclear deal last year. Trump said that deal was not restrictive enough and he wants a new agreement that would limit Iran’s ballistic missile program and its support for terrorism in the region.
Trump has vacillated between bellicose rhetoric suggesting a military response and a softer tone emphasizing his desire to avoid war.
Critics say that Trump's aggressive sanctions regime has caused the current crisis, with Iran lashing out in response to what it calls "economic warfare." Democrats in Congress warn that a military strike could lead to all-out war that will cost American lives and disrupt major segments of the oil production system. They said Trump should seek congressional authorization before taking any such step.
"We need to have a conversation as a country and as a Congress about whether or not this is an attack so directly relevant to America's interests as to justify military action," said Sen. Chris Coons, D- Del., speaking on CNN.
I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!— Donald J. Trump (@realDonaldTrump) September 18, 2019
Contributing: Associated Press
This article originally appeared on USA TODAY: Trump says he will hit Iran with new sanctions over Saudi oil attack