United States President Joe Biden said negotiating a nuclear deal with Iran through diplomacy would be included in his first set of discussions as president.

The U.S. president, who was sworn into office on Wednesday, hopes to hold early talks about the deal with foreign counterparts and allies.

Biden is seeking to extend and strengthen restrictions on Iran’s nuclear program, and said that if Tehran returned to full compliance with the 2015 nuclear deal, Washington would do the same.

Britain, France and Germany sent a stern warning to Iran not to continue on with the development of uranium metal-based fuel for a research reactor, saying the move was in breach of the 2015 nuclear agreement.

Last week, the U.N.’s nuclear watchdog, the International Atomic Energy Agency, confirmed the Iranian government had started developing the fuel.

The three powers, who remain parties to the deal, which is also known as the Joint Comprehensive Plan of Action (JCPOA), with China and Russia, said they were “deeply concerned” by the production of the uranium metal.

And UK Prime Minister Boris Johnson said the British government was working “virtually around the clock” to secure the release of detained British-Iranian dual national Nazanin Zaghari-Ratcliffe and other dual nationals arbitrarily detained in Iran.

Speaking in Parliament, Johnson said, “We’re doing everything we can to secure the (end to) what we regard as the completely unjustified detention in Tehran of Nazanin Zaghari-Ratcliffe.”

Ms. Zaghari-Ratcliffe was sentenced to five years’ imprisonment in 2016 for “plotting to topple the Iranian government,” a charge she has always denied.