The US has imposed sanctions on Iran's central bank following last weekend's attack on Saudi Arabia's oil facilities.
President Donald Trump made the move on Friday as US Treasury Secretary Steven Mnuchin said the bank was Tehran's last source of funds.
The US administration has blamed Iran for the Saudi attacks.
Speaking in the Oval Office during a meeting with Australian Prime Minister Scott Morrison, Mr Trump said: "We have just sanctioned the Iranian national bank."
Iran denies being involved in the attack. The attacks and recriminations are increasing fears of an escalation in the region.
Mr Mnuchin says the latest sanctions demonstrate the US is continuing a maximum pressure campaign, asserting "we have now cut off all funds to Iran".
The announcement comes as the Pentagon is expected to present a range of military options to Mr Trump as he considers how to respond to an attack on Saudi's oil industry.
The president will be given a list of potential airstrike targets inside Iran, among other possible responses, at a White House meeting, and he also will be warned that military action against the Islamic Republic could escalate into war, US officials familiar with the discussions told the Associated Press.
The national security meeting will likely be the first opportunity for a decision on how the US should respond to the attack on a key Middle East ally.
Any decision may depend on what kind of evidence the US and Saudi investigators are able to provide to prove that the cruise missile and drone strikes were launched by Iran, as a number of officials, including Secretary of State Mike Pompeo, have asserted.
The Iran-backed Houthi rebels in Yemen said they carried out the pre-dawn attacks on Saudi Aramco's Abqaiq oil processing complex and Khurais oilfield last Saturday, but a US official told The National the strikes appeared to have been launched from the direction of Iran to the north-west, not Yemen in the south. Saudi Arabia on Wednesday presented debris of Iranian-made missiles and drones used in the attacks that it said clearly showed Tehran's involvement, although defence ministry spokesman Colonel Turki Al Malki stopped short of saying they were launched from Iran.
A forensic team from US Central Command is examining the missile and drone debris, but the Pentagon said its assessment is not finished. Officials are trying to determine if they can get navigational information from the debris that could provide hard evidence that the strikes came from Iran.
Pentagon spokesman Jonathan Hoffman said on Thursday that the US had a high level of confidence that officials will be able to accurately determine exactly who launched the attacks last weekend.
Besides Saudi and US investigators, evidence from the attacks is also being examined by military experts from France. The French defence ministry said they include specialists in explosives, missile trajectory and ground-to-air defence systems.
Iran has denied involvement and warned the US that any attack will spark an "all-out war" with immediate retaliation from Tehran.
Both Mr Pompeo and Vice President Mike Pence have condemned the attack on Saudi oil facilities as "an act of war".
The attacks knocked out half of Saudi Arabia's oil production and briefly sent oil prices surging when markets reopened at the start of the week. Saudi Arabia has said it is confident of restoring full production capacity by the end of the month.
Aramco officials on Saturday showed journalists the damage caused at Khurais, where four strikes left the web of pipes and burnt and warped and peppered with shrapnel. There were no casualties among the 200-300 staff present at the time, said Fahad Al Abdulkareem, a general manager at the state-controlled oil company.
Mr Pompeo visited Saudi Arabia on Wednesday to discuss the attacks with Crown Prince Mohammed bin Salman before flying to the UAE the next day for talks with Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces.
He said Washington prefers a peaceful resolution to the crisis.
However, Mr Pence said Mr Trump will "review the facts, and he'll make a decision about next steps. But the American people can be confident that the United States of America is going to defend our interest in the region, and we're going to stand with our allies".
The US response could involve military, political and economic actions, and the military options could range from no action at all to airstrikes or less visible moves such as cyberattacks. One likely move would be for the US to provide additional military support to help Saudi Arabia defend itself from attacks from the north, since most of its defences have focused on threats from the Houthi rebels in Yemen to the south.
With security concerns mounting in the region, Kuwait raised the security levels at its ports, the Kuwait News Agency reported on Friday. The emirate's armed forces had already raised their security levels after the September 14 attacks.
General Joseph Dunford, chairman of the Joint Chiefs of Staff, has said the question of whether the US responds to the attacks is a "political judgement" and not for the military.
"It is my job to provide military options to the president should he decide to respond with military force," Gen Dunford said.
Mr Trump will want "a full range of options", he said. "In the Middle East, of course, we have military forces there and we do a lot of planning and we have a lot of options."
Elissa Slotkin, a Democratic congresswoman and a former Middle East policy adviser for the Pentagon, said on Thursday that if Mr Trump "chooses an option that involves a significant military strike on Iran that, given the current climate between the US and Iran, there is a possibility that it could escalate into a medium to large-scale war, I believe the president should come to Congress".
Ms Slotkin said she hoped Mr Trump considered a broad range of options, including the most basic choice, which would be to place more forces and defensive military equipment in and around Saudi Arabia to help increase security.
US officials are unwilling to predict what kind of response Mr Trump will choose. In June, after Iran shot down an American surveillance drone, the president initially endorsed a retaliatory military strike then abruptly called it off because he said it would have killed dozens of Iranians. The decision underscored the his long-held reluctance to embroil the country in another war in the Middle East.
Instead, Mr Trump opted to have US military cyber forces carry out a strike against military computer systems used by Iran's Revolutionary Guard to control rocket and missile launchers, according to US officials.
The Pentagon said the US military was working with Saudi Arabia to find ways to provide more protection for the northern part of the country.
Air Force Col Pat Ryder, spokesman for the Joint Chiefs of Staff, told Pentagon reporters on Wednesday that Centcom was talking with the Saudis about ways to mitigate future attacks. He would not speculate on what types of support could be provided.
Other US officials have said adding Patriot missile batteries and enhanced radar systems could be options, but no decisions have been made.