U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif start another round of talks on Tehran’s nuclear program on March 2.
U.S. Energy Secretary Ernest Moniz is due to join the discussions in Montreux, Switzerland.
U.S. officials say talks between Washington and Tehran have progressed but that difficult issues remain.
The United States and five other powers are seeking a deal with Iran under which Tehran would limit its nuclear program in exchange for the gradual easing of economic sanctions.
The West fears Iran wants to develop a nuclear weapons program, something Tehran denies.
The sides are facing an end-of-March deadline for a framework nuclear agreement.
The talks in Switzerland come with Israeli Prime Minister Benjamin Netanyahu due to speak against a potential deal before the U.S. Congress on March 3.
Zarif has accused Netanyahu of trying to undermine the talks.
The Obama administration has also criticized the timing of Netanyahu’s address.
The White House was not consulted before the invitation to Netanyahu was given by Republic lawmakers.
Netanyahu disapproves of a potential deal now being negotiated by Iran and six world powers, including the United States.
The Israeli leader claims the deal will not prevent Tehran from being able to build an atomic bomb.