WASHINGTON — The Biden administration said Sunday it remains open to talks with Iran over the 2015 nuclear deal despite Tehran’s rejection of an EU invitation to join a meeting with the U.S. and the other original participants in the agreement.

A senior administration official said the U.S. was “disappointed” in the rejection but was flexible as to the timing and format of the talks and saw Iran’s decision to snub the European invitation as part of the diplomatic process. The official said the U.S. would be consulting with the other participants — Britain, China, France, Germany, Russia and the European Union — on the way forward.

The official was not authorized to discuss the matter by name and spoke on condition of anonymity.

Earlier Sunday, Iran turned down the offer for talks saying the “time isn’t ripe” for the meeting, at which the U.S. would have participated as an observer. Iran had been insisting that the U.S. lift or ease sanctions imposed on it by the Trump administration under its “maximum pressure campaign” before sitting down with the United States.

President Joe Biden has said repeatedly that the U.S. would return to the deal that his predecessor, Donald Trump, withdrew from in 2018 only after Iran restores its full compliance with the accord.

“Considering US/E3 positions & actions, time isn’t ripe for the proposed informal meeting,” Iranian foreign ministry spokesman Saeed Khatibzadeh said on Twitter.