Iranian President Hassan Rouhani said on Sunday that if the United States quits the nuclear deal between Tehran and world powers Washington would regret it “like never before.”

The Trump administration is fast approaching a self-imposed deadline on whether or not to leave the deal if it is not altered to place further restrictions on Iran’s nuclear program to prevent the country from obtaining nuclear weapons.

“If the United States leaves the nuclear agreement, you will soon see that they will regret it like never before in history,” Rouhani said in a televised speech in northwestern Iran.

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He also said Iran had plans in place to respond to anything the US might do.

“Necessary directives have been given to related organizations and the Atomic Energy Organization of Iran,” should the US go ahead with its threat to withdraw, he said.

Iran has warned in the past it could quickly restart its nuclear program should the US pull out of the accord.

US President Donald Trump has set a May 12 deadline to “fix or nix” the deal, formally known as the Joint Comprehensive Plan of Action. The agreement imposes strict restrictions on Iran’s nuclear program in return for the loosening of economic sanctions.

In January, Trump gave Congress and European allies an ultimatum to either amend the pact to his liking or stand by as he renewed sanctions against Tehran.

Britain, France and Germany — the three European countries that signed the deal — have repeatedly tried to persuade Trump not to abandon it. The other two signatories are Russia and China who both back Iran in maintaining the agreement.

Trump has pilloried the agreement designed to curb Iran’s nuclear program as “insane” and “ridiculous” and called for fresh measures to counter Iran’s ballistic missile program and support for militant groups across the Middle East.

Iran has repeatedly insisted it is sticking to the nuclear deal and will not negotiate further over its missile program.

Last week, an Israeli satellite imaging company released images showing what it described as “unusual” movement around the Iranian Fordo nuclear facility, a one-time uranium enrichment plant buried deep underground that was converted to a research center as part of the 2015 nuclear deal.

The photographs, which show large numbers of vehicles at the entrance to the facility and other signs of increased activity there, did not in themselves indicate any violation of the nuclear accord.

However, some have read the increased activity as an attempt by the Islamic Republic to imply that it is prepared to begin enriching uranium at the site if the US pulls out of the agreement.