US Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif met for six-hour talks on Saturday aimed at resolving the remaining differences over the Iran nuclear deal.

Just weeks ahead of the June 30 deadline for a final and comprehensive agreement to settle the 12-year standoff on the Iran nuclear problem, a diplomatic source said there are still some issues and that the talks on Saturday ended without any big breakthrough.

Asked about completing the full accord by June 30, Zarif said, "We will try."