LONDON (Reuters) – Iran can resume production of highly enriched uranium within five days if the nuclear deal it struck with world powers in 2015 is revoked, Iran’s atomic chief was quoted by state media as saying on Tuesday.

The deal that Iranian President Hassan Rouhani championed with the United States, Russia, China and three European powers led to the lifting of most sanctions against Tehran in return for curbs on its nuclear program.

Rouhani has intensified efforts to protect the deal, also known by its acronym JCPOA, against Washington’s return to an aggressive Iran policy, after U.S. President Donald Trump approved new sanctions on Tehran.

Rouhani warned last week that Iran could abandon the nuclear agreement “within hours” if the United States imposes any more new sanctions.

“The president’s warning was not baseless,” Head of Atomic Energy Organization of Iran, Ali Akbar Salehi said on Tuesday.

“If we decide, we can reach 20 percent (uranium) enrichment within five days in Fordow (underground nuclear plant),” he added.

However, Salehi who was reappointed this month as vice president and the head of the Atomic Energy Organization, said his main priority would be to protect the JCPOA.

Following the nuclear deal, Iran drastically reduced the number of centrifuges – machines that enrich uranium – installed at Fordow, and kept just over 1,000 there for research purposes.

The JCPOA states that no enrichment is permitted at Fordow for 15 years.

Uranium enriched to a high level can be used to make an atomic bomb. Iran says its nuclear program is for peaceful purposes.

The U.S. Treasury imposed sanctions on six Iranian firms in late July for their role in the development of a ballistic missile program after Tehran launched a rocket capable of putting a satellite into orbit.

Trump also signed in August a U.S. Senate bill that imposed sanctions on Iran, Russia, and North Korea.

Iran says new U.S. sanctions breach the JCPOA but the United States says they were unrelated to the deal.

During his election campaign Trump called the deal a “disaster” and “the worst deal ever negotiated”. This month he said he did not believe Iran was living up to the deal’s spirit.

(Reporting by Bozorgmehr Sharafedin; Editing by Matthew Mpoke Bigg)