TEHERAN (AFP) - Foreign Minister Mohammad Javad Zarif said on Thursday his talks in Switzerland with US Secretary of State John Kerry on Iran's nuclear programme are making progress although "a lot of work" remains.

"We are advancing very well but there's still a lot of work to be done," he told Iran's state news agency IRNA in the Swiss city of Lausanne on the fourth day of the nuclear negotiations.

His assessment echoed that of Kerry, who said the talks were facing "tough issues" but "progress" was being made ahead of a March 31 deadline for the outlines of a major deal.