US Secretary of State John Kerry will hold talks on Iran’s nuclear program with his French, German and British counterparts Saturday in Paris, a US official said, as negotiations over a deal gather pace.

US Secretary of State John Kerry will hold talks on Iran's nuclear program with his French, German and British counterparts Saturday in Paris, a US official said, as negotiations over a deal gather pace.

Pointing out that "tough challenges" had yet to be resolved before a March 31 deadline for the deal, the senior State Department official said Wednesday the United States and Iran would also resume joint talks on March 15. The comments came as Kerry wrapped up a new round of talks with his Iranian counterpart Mohammad Javad Zarif in Switzerland.