U.S. and Iranian nuclear experts continuing talks in the Swiss city of Lausanne on March 18 in a push for deal to curb Iran's nuclear program.
The delegations are led by U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif.
"We are trying to overcome the differences," Zarif told reporters. "We can make progress if the other party shows political will."
U.S. officials said that progress had been made on technical issues under discussion, but that gaps must still be bridged.
The United States and five other powers are seeking a deal to rein in Iran's nuclear program, which Western nations fear may be aimed at developing atomic weapons, in exchange for sanctions relief.
The sides have set an end-of-March deadline for a framework agreement, with a final deal to follow by June 30.