U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif have held two hours of talks on Tehran's disputed nuclear program.
The meeting on February 22 in Geneva included for the first time U.S. Secretary of Energy Ernest Moniz and Iran's nuclear chief Ali Akbar Salehi.
The two spent most of the day separately negotiating technical details of curbing Iran's nuclear program.
Zarif told Iranian state media that midlevel bilateral talks had produced "good discussions but no agreements" and that some differences remained.
Zarif said the inclusion of Moniz and Salehi reflected a need "for higher level people with all-embracing command over all issues."
Kerry on February 21 cautioned against reading too much into the presence of Moniz in Geneva, which U.S. officials said was decided after Iran announced Salahi would attend.
Kerry and Zarif are due to meet again later on February 23.
World powers and Iran have set an end-of-March deadline for a framework agreement, with four further months for the technical work to be ironed out.
Iran's negotiations with the P5+1 group -- the United States, Britain, France, Germany, Russia, and China -- have already missed a November 2014 target date.
U.S. President Barack Obama has said a further extension would make little sense without a basis for continuing discussions.
Kerry said on February 21 that there was no doubt Obama was serious.
Obama, Kerry said, "is fully prepared to stop these talks if he feels that they're not being met with the kind of productive decision-making necessary to prove that a program is, in fact, peaceful."
Zarif said Iranian President Hassan Rohani would not accept a small short-term agreement, nor a broad accord that left room for interpretation.
Israeli Prime Minister Benjamin Netanyahu said on February 22 that it was "astonishing" that the talks, which he said could end by allowing Iran "to develop the nuclear capabilities that threaten our existence," were proceeding.