US Secretary of State John Kerry has met his Iranian counterpart Mohammad Javad Zarif in Switzerland less than one week before an end-of-month deadline to secure a nuclear deal.
Kerry and Zarif and their teams met on Thursday in the Swiss resort town of Lausanne on Lake Geneva trying to overcome still significant gaps, after nearly two years of negotiations.
Ahead of the March 31 deadline, Iranian President Hassan Rouhani spoke with the leaders of France, Britain, China and Russia in an apparent effort to break an impasse holding up a nuclear deal between Tehran and major world powers.
Rouhani also raised the divisive issue of Yemen, where a Saudi-led coalition has launched air strikes on Shia Houthi rebels.
Al Jazeera's Diplomatic Editor James Bays, reporting from Lausanne, said both the US and Iranian delegations had expressed confidence about a positive outcome of the nuclear talks.
Despite the Yemen tensions, which has the US and Iran supporting the opposing sides of the conflict, Bays said that negotiators had been careful to focus only on the nuclear deal.
As an indication that progress is being made, French Foreign Minister Laurent Fabius is reportedly joining Kerry and Zarif in Switzerland on Friday, he added.
The top diplomats from Britain, China, Germany and Russia are expected to join the talks if the US and Iran are close to an agreement.
En route to Switzerland with Kerry on Wednesday, one official said the American side "can see a path forward to get to agreement'' by the end of March.
The seven nations have set themselves a March 31 deadline for the outline of a final accord they hope to seal by the end of June.
Both President Barack Obama and Iran's Ayatollah Ali Khamenei have spoken against what would be a third extension of the talks.
Opponents of a nuclear deal, among them wary American allies in the Middle East and hardliners in Iran and in Congress, stand ready to complicate the process if negotiators cannot reach a breakthrough in the next six days.
American lawmakers have threatened new sanctions on Iran as well as the establishment of a process which would allow them to vote down any final accord.
The United States and its partners are trying to get Iran to cut the number of centrifuges it uses to enrich uranium, material that can be used in warheads, and agree to other restrictions on what tehran
insists is a peaceful nuclear programme.