U.S. Secretary of State John Kerry (centre left) talks to an aide outside the Beau-Rivage hotel during a break in negotiations over Iran's nuclear program in Lausanne, Switzerland, March 17, 2015. Iran and the United States have agreed on 90 percent of nuclear technical issues. Reuters

Iranian negotiators reported talks between Iran and six world powers regarding Tehran's nuclear program made great progress Tuesday, and there was a chance agreement could be reached before day's end. The comments followed earlier statements by western diplomats pessimistic agreement on a framework for a final deal could be reached before a self-imposed March 31 deadline.

"We have agreed on 90 percent of the technical issues," Ali Akbar Salehi, the head of the Iranian Atomic Energy Organization, was quoted saying by the state television, according to Agence France-Presse. "In most of the issues we have come to mutual agreements -- we have differences only in one major issue which we will try to solve in this evening's meeting.”

The Iranian nuclear chief said an agreement between U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif before the day is out is possible. Zarif and Kerry met Monday for nearly five hours to discuss the possibility of easing Western sanctions in exchange for halting some of Iran’s controversial nuclear programs. Zarif then left for Brussels to meet European foreign ministers and EU foreign policy chief Federica Mogherini. The two diplomats -- along with representatives from Britain, France, Germany, Russia and China -- met again in Lausanne, Switzerland, Tuesday to resume their dialogue.

Earlier, a senior Western diplomat said Kerry and his delegates shared other negotiators’ pessimism the talks would conclude quickly. "We'll see what happens the rest of the week but for now we're not there," a senior Western diplomat said, according to Reuters. Zarif and Salehi have been more optimistic than their Western counterparts throughout the talks. The six parties have set a June 30 deadline for a final accord. No further comment has been made on the progress of the talks by U.S. officials or the other Western diplomats.

Tehran has been accused of using its nuclear program to produce weapons-grade uranium and global efforts have called for Iran to stop its uranium enrichment. The Iranian government has denied any intention of building weapons, and claimed its programs are only used for energy, medical and scientific goals.