Negotiators in talks on Iran's nuclear program have reported some progress but said a lot of work remains to secure a deal.
Two days of talks between senior U.S. and Iranian diplomats ended on February 23 in Geneva, where officials from the six powers and Iran also met.
Russia's negotiator, Deputy Foreign Minister Sergei Ryabkov, said after the talks ended that there is "growing confidence" that Tehran and six world powers will reach a comprehensive accord by a June 30 deadline.
"We are satisfied to see every new meeting achieve further progress," he added.
Wang Qun of the Chinese Foreign Ministry said, "The key parties, especially Washington and Tehran, are moving closer toward each other...as far as uranium enrichment is concerned.
“This reflects the strong sentiment from both capitals for an agreement," he added.
Iranian Foreign Minister Mohammad Javad Zarif earlier said the talks were "useful, constructive, and serious" but that there is still a "long way" to go.
Zarif, who met directly with U.S. Secretary of State John Kerry during portions of the negotiations, said the talks would resume in Switzerland on March 2.
A senior U.S. administration official at the talks said "some progress" had been made and that the six world powers and Iran had been able to "sharpen up some of the tough issues" that need resolving.
U.S. Energy Secretary Ernest Moniz and Iranian nuclear chief Ali Akbar Salehi were also involved in the talks along with Helga Schmid, political director of the European Union's External Action Service.
The United States, Russia, China, Britain, France, and Germany are seeking an agreement with Tehran that would rein in Iran's nuclear program in exchange for relief from economic sanctions.
Tehran dismisses Western suspicions it is using its civilian nuclear program to also secretly develop nuclear weapons.
After missing two self-imposed deadlines last year, negotiators are seeking a political framework by the end of March and a full deal by June 30.
The 12-year-old dispute over Iran's nuclear program has added to tensions in the Middle East.
Diplomatic activity has intensified as the new deadlines approach.
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.
He said Obama "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.
Obama is under pressure from critics at home and from Israeli Prime Minister Benjamin Netanyahu, who has warned against any deal that might fail to prevent Iran from developing nuclear weapons.
Netanyahu said on February 22 that the talks could end by allowing Iran "to develop the nuclear capabilities that threaten our existence" and that it was "astonishing" they were continuing.