Kerry added that Iran and P5+1 group reached real progress in their talks and are planning to return to negotiations next week.
Since November 2013, Iran and the P5+1 group of Russia, the United States, China, the United Kingdom, France and Germany, have been negotiating a long-term nuclear agreement guaranteeing the peaceful nature of Tehran's nuclear program.
The sides agreed to reach a final comprehensive deal by July 2015.
John Kerry said he will travel to London later in the day to discuss Iran nuclear talks with his counterparts from Britain, Germany, and France.
The top US diplomat was speaking at a press conference following the end of the Friday round of negotiations with Iran in Lausanne, Switzerland, which was aimed at curbing Tehran's uranium enrichment program.
Kerry told reporters he was to leave for London, from whence he would then fly to Washington. He also plans to meet with EU foreign policy chief Federica Mogherini in the UK capital.