US Treasury Secretary Steven Mnuchin said on April 11 that the US may impose “very strong” sanctions on Iran.

His remarks came as the multilateral parties trying to formulate a possible amended nuclear deal acceptable to both Donald Trump and the Islamic Republic found themselves with just one month to go before the US President’s May 12 “last chance” deadline for an adjusted accord palatable to his administration.

Mnuchin referred to “primary and secondary sanctions” that could be introduced against Tehran, referring to penalties against the country itself and entities that do business with the Iranians. The Treasury chief spoke to reporters after testifying before a House appropriations subcommittee. His words will do nothing to assuage fears that Trump, having added more hawkish advisors to his administration in recent weeks including national security advisor John Bolton, is preparing to withdraw the US from the deal, also adopted by the UK, France, Germany, Russia and China, along with Iran, in October 2015.

The deal, formally known as the Joint Comprehensive Plan of Action (JCPOA) and implemented from January 16, 2016, withdrew crippling sanctions against Iran’s oil exports, central bank activities and other areas in return for measures designed to block Iran’s path to the development of a nuclear weapon for a decade. Mnuchin told reporters he was talking about a possible fresh round of sanctions, as well as the return of the sanctions waived under the nuclear deal.

“If the president doesn’t sign the certification, the sanctions snap back into place,” Mnuchin said, according to Bloomberg. “I do think the primary and secondary sanctions would have an important impact on the Iranian economy, and that’s something he’s thinking about and balancing as he makes his decision.”

As for additional sanctions independent of the nuclear deal, Mnuchin told reporters “you can assume we continue to do work on that”.

The Trump administration has accused Iran of causing instability and violence across the Middle East, thereby breaking “the spirit” of the JCPOA. However, apart from the US, the signatories say they are confident Iran has followed the letter of the deal. Having been painstakingly negotiated to provide benefits that were materialising—for instance, Iran’s confirmed cooperation in not pursuing a nuclear bomb—it should be retained with all the signatories’ participation, they say.

On April 9, Iranian President Hassan Rouhani said Trump will seriously regret it if he violates the multilateral nuclear accord. In a televised speech given at a conference in Tehran during Iran’s National Nuclear Technology Day—which unveiled some of the country’s latest achievements in its civil nuclear sector—Rouhani said: “The new US president—who makes big claims and has many ups and downs in his words and behaviour—has been trying for 15 months to break the JCPOA... but the structure of the JCPOA is so strong that it has not been shaken by such quakes.”

He added: “Iran will not violate the nuclear deal, but if the United States withdraws from the deal, they will surely regret it. Our response will be stronger than what they imagine, and they would see that within a week.”