Russia’s foreign minister has said prospects of a preliminary agreement on Iran’s nuclear programme are “very good” on the final day of negotiations.

Sergei Lavrov said he was rejoining the talks in Switzerland on Tuesday, suggesting they were close to a deal.

Marathon negotiations between Iran and foreign ministers from six world powers are nearing a self-imposed deadline.

Ministers want to restrict Iran’s nuclear programme in exchange for relief from crippling sanctions.

There is no sign that the most intractable problems, such as the pace and timing of sanctions relief, have been resolved, the BBC’s Barbara Plett reports from Lausanne.

However, reports say there are plans to issue a joint statement on general points of agreement, accompanied by documents outlining more technical details.

These would be enough for all parties to continue negotiations aimed at achieving a comprehensive accord in June, our correspondent adds.

‘Cautiously optimistic’

Mr Lavrov announcement that he was rejoining negotiations followed a statement, as he left the talks on Monday, that he would only return if there was a realistic chance of securing an agreement.

“I believe that the prospects are very good and promising,” he told a news conference on Tuesday.