Iran's President Hassan Rouhani says that progress made in nucleartalks means a final deal can be reached.
"There is nothing that cannot be resolved," although some differences still remain, Iranian state media quoted him as saying.
US Secretary of State John Kerry also said that "substantial progress" had been made in the talks.
Six world powers are negotiating a deal with Iran aimed at limiting its nuclear activity, with a late March deadline.
Iran insists its nuclear programme is for peaceful purposes but world powers fear it has military ambitions.
Mr Rouhani said that in the current round of talks in Lausanne, Switzerland, "shared points of view emerged in some of the areas where there had been a difference of opinion".
They could become "a foundation for a final agreement", he said, according to state news agency Irna.