LAUSANNE, Switzerland — Iran and Russia’s foreign ministers said April 1 that political agreement on major elements of a final Iran nuclear accord might be announced here later in the day, and said that they hoped negotiators and experts would then move on to the work of drafting the detailed final Iran nuclear accord due at the end of June. But French and British envoys said while progress had been made, it was slow-going, and the United States so far withheld comment on whether it considered sufficient progress had been made.

“We have made significant progress over the last few days but it has been slow-going,” British Foreign Secretary Philip Hammond said April 1.

“We decided to break last night because some of the staff had been working through the previous night,” Hammond told the BBC here after talks resumed in the morning April 1. “I’m optimistic that we will make further progress this morning but it does mean the Iranians being willing to meet us where there are still issues to deal with. Fingers crossed and we’ll hope to get there during the course of the day.

“I think we have a broad framework of understanding but there are still some key issues that have to be worked through,” Hammond added. “Some of them are quite detailed and technical so there is still quite a lot of work to do, but we are on it now and we’ll keep going at it.”