WASHINGTON - US President Joe Biden campaigned on restoring an accord limiting Iran’s nuclear programme. It remains unclear if Tehran, which is demanding that sanctions be lifted first, will accept the offer to talk.

The United States took a major step on Thursday toward restoring the Iran nuclear deal that the Trump administration abandoned, offering to join European nations in what would be the first substantial diplomacy with Tehran in more than four years, Biden administration officials said.

In a series of moves intended to make good on one of President Biden’s most significant campaign promises, the administration also backed away from a Trump administration effort to restore United Nations sanctions on Iran. That effort had divided Washington from its European allies.

And at the same time, Secretary of State Antony J. Blinken told European foreign ministers in a call on Thursday morning that the United States would join them in seeking to restore the 2015 nuclear accord with Iran, which he said “was a key achievement of multilateral diplomacy.”

While it was unclear whether the Iranians would agree to join discussions, three people familiar with the internal debate said it was likely Iran would accept. The officials said Iran would probably be more open to a meeting with the European Union, where the United States was a guest or observer, rather than direct formal talks with Washington as a participant.

In recent days, the Iranian foreign minister, Mohammad Javad Zarif, and President Hassan Rouhani have suggested they were open to discussing some kind of synchronized approach, in which both sides would act on a certain date. That has an appeal inside the White House, one senior American official said, noting it was how key steps for carrying out the original 2015 deal were coordinated.

But with an Iranian presidential election only four months away, it was not clear if the country’s supreme leader, Ayatollah Ali Khamenei, and the nation’s political and military leadership would fully support re-engagement with the United States.