Iran said it had not seen enough incentives from the European Union to pave the way for a deal over its "nuclear activities", ahead of a new round of talks next week.
Top negotiator Cyrus Nasseri warned that Tehran would pull out of the talks with the so-called EU3 without tangible progress, but said nevertheless that the negotiations were on the right track.
He told the official IRNA news agency that the European offers in the negotiations, aimed at allaying international concerns Iran is trying to build a nuclear bomb, were not enough.
"We don't have much time for reaching a solution, time is limited and we will halt (negotiations) as soon as we feel we are not making tangible progress," Nasseri said ahead of a new round of discussions on April 19.
However "the negotiations are on the right track ... leading to a wise, logical and balanced solution satisfactory to both sides," he added.
