The agreement, seen by Reuters, listed a series of steps to be taken by Iran to ensure greater transparency in its disputed nuclear programme, also including "managed access" to a uranium mine and a heavy water plant.
The measures will be implemented within three months, the agency said.
Speaking at a news conference with United Arab Emirates (UAE) Foreign Minister Sheikh Abdullah bin Zayed al-Nahayan in Abu Dhabi, Kerry said the major powers were "unified on Saturday when we presented a proposal to the Iranians, and the French signed off on it, we signed off on it, and everybody agreed it was a fair proposal. There was unity, but Iran couldn't take it at that particular moment, they weren't able to accept that particular thing."