Secretary of State John Kerry says there has been "genuine progress" on talks with Iran over its nuclear program, but he has acknowledged that gaps still remain as the negotiations go on a brief hiatus before resuming next week.

Speaking with reporters in Lausanne, Switzerland, where the so-called "P5+1" nations — the U.S., Russia, China, Britain, France and Germany — were meeting to hammer out a deal before the end of the month, Kerry insisted that "we are not rushing" on an agreement.

NPR's Peter Kenyon, reporting from Lausanne, remarks that "critics say the negotiators are too eager for a deal, but this week a European diplomat described the sides as 'not close' to an accord."

However, Kerry, who was ready to depart for London, said: "This has been a two and a half-year process. But we recognize that fundamental decisions have to be made now and they don't become easier as time goes by."

The U.S. secretary of state will return to Lausanne on Wednesday "to determine whether or not an agreement is possible."

Kerry's comments were largely echoed by Iranian President Hassan Rouhani, who was quoted by the official IRNA news agency as saying progress made in the latest round of discussions could be the basis of a deal.

Peter reports that "maintaining unity within the P5+1 will be crucial as talks resume Wednesday, facing an end of March deadline to reach a framework agreement."

Update at 1:25 p.m. ET. Khamenei: After Deal, Sanctions Should End 'With No Delay':

In a speech today, Iran's Supreme Leader Ali Hosseini Khamenei said:

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