These are the highest sanctions ever imposed on a country, Donald Trump

President Donald Trump on Friday announced new sanctions on Iran that he said were the toughest-ever against another country but indicated he did not plan a military strike, calling restraint a sign of strength.

The Treasury Department unveiled action against Iran's central bank after US officials said that Tehran carried out weekend attacks on rival Saudi Arabia's oil infrastructure which triggered a spike in global crude prices.

"We have just sanctioned the Iranian national bank," Trump told reporters in the Oval Office. "These are the highest sanctions ever imposed on a country."

But Trump indicated he did not plan a military response, attacking both critics who thought the mogul turned president would trigger war and hawks seeking a military response.

"The easiest thing I could do (is) knock out 15 different major things in Iran," Trump said.

"I could do it right here in front of you. And that would be it. And then you would have a nice, big story to report," he said.

"But I think the strong-person approach and the thing that does show strength would be showing a little bit of restraint," he said.

"Much easier to do it the other way. It's much easier. And Iran knows if they misbehave, they're on borrowed time," he said.

New ground for sanctions

The United States already maintains sweeping sanctions on Iran including on its central bank, with anyone who deals with it subject to prosecution, due to Tehran's alleged nuclear program.

But the Treasury Department said that it was imposing sanctions for the additional reason of "terrorism," saying the central bank had provided "billions of dollars" to two forces blacklisted by the United States.

Such a designation may be more difficult to lift, even if Trump loses next year's election to a Democrat who wants to ease sanctions as part of a future deal.

"Iran's brazen attack against Saudi Arabia is unacceptable," Treasury Secretary Steven Mnuchin said in a statement.

"Treasury's action targets a crucial funding mechanism that the Iranian regime uses to support its terrorist network, including the Qods Force, Hezbollah and other militants that spread terror and destabilize the region," he said.

The Qods Force conducts international operations for Iran's elite Revolutionary Guards, who are in charge of protecting the clerical regime.

Hezbollah, the Shiite militant group and political party in Lebanon, is among Iran's closest regional partners.

Behnam Ben Taleblu, a senior fellow at the Foundation for the Defense of Democracies, which supports tough action on Iran, said that the latest measures are a way "to push Tehran to shun funding terrorism."

"It proves to Tehran that there will be no stopping US sanctions unless Iran changes its behavior," he said.

The United States also imposed sanctions on Iran's sovereign wealth fund, whose board of trustees includes President Hassan Rouhani, as well as Etemad Tejarate Pars, a company that the Treasury Department said had sent money internationally on behalf of Iran's defense ministry.

Trump in June authorized a military strike after Iran shot down a US drone, only to call it off at the last moment.

He recently said that he hopes for talks with Rouhani, which responded that Trump must first ease sanctions.

Trump last year pulled out of a nuclear accord with Iran negotiated under former president Barack Obama, sending tensions soaring as he tried to stop all countries from buying Iran's oil.