A landmark deal with world powers on Iran's controversial nuclear programme is an "important achievement" but only a "first step" towards a final accord, its Foreign Minister Mohammad Javad Zarif said Sunday. "This is only a first step. It is an important achievement but it is a first step," Zarif told reporters. He saidthe accord had a "clear reference that enrichment will continue" -- an issue long seen as a stumbling block to a deal.