Iran nuclear talks make substantial progress: Kerry

US Secretary of State John Kerry on Saturday said that "substantial progress" has been made in negotiations over Iran's nuclear programme.

Kerry's remarks came a day after the P5+1 countries -- the US, China, Russia, France, Britain, plus Germany -- and Iran suspended their week-long negotiations, without having reached a framework agreement ahead of the March 31 deadline, according to a Xinhua report.

"We have not yet reached the finish line, but make no mistake, we have the opportunity to try to get this right," Kerry said at press conference in the Swiss city of Lausanne, where a series of intensive multilateral and bilateral talks were held to bridge the gaps over Tehran's nuclear programme.

Kerry said that the US was not rushing for an agreement, but it was time to make hard decisions.

"We recognise that fundamental decisions have to be made now and they don't get any easier as time goes by," he noted.

The top US negotiator will leave for London later to meet his counterparts from Britain, Germany, and France, and the high representative of the European Union (EU) to resolve the remaining sticking points.

The nuclear negotiations will be resumed in Lausanne later next week. The parties involved in the negotiations had extended the talks in November last year and are hoping for a comprehensive pact by the end of June this year.