Foreign Minister Mohammad Javad Zarif said Thursday his talks in Switzerland with US Secretary of State John Kerry on Iran’s nuclear program are making progress although "a lot of work" remains.

Foreign Minister Mohammad Javad Zarif said Thursday his talks in Switzerland with US Secretary of State John Kerry on Iran's nuclear program 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.

The Iranian negotiators are in talks with their US and European counterparts in Lausanne since Sunday.

Zarif to stay in Lausanne 'as long as required'

Foreign Minister Mohammad Javad Zarif said Thursday that he will stay in Lausanne as long as it is required to negotiate over a deal on Iran's peaceful nuclear program.