Iranian Foreign Minister Mohammad Javad Zarif on Sunday said nuclear talks with world powers were progressing slowly and urged all sides to avoid "troublesome" issues.
Zarif also agreed with EU foreign policy chief Catherine Ashton that the technical talks on how to implement a landmark nuclear deal would resume after the Christmas holidays, media reported.
Zarif and Ashton made the decision during a telephone call to discuss the expert-level talks that began on Thursday between Iran and delegates from the six major powers known as the P5+1.
The negotiations, which are aimed at setting a framework and a timeline for the nuclear accord clinched last month, stretched into a fourth day in Geneva on Sunday.
ISNA news agency said Zarif and Ashton discussed the latest developments at the talks and agreed they would resume after Christmas break. It provided no further details.
But at a joint news conference with visiting Italian Foreign Minister Emma Bonino, Zarif said little progress had been made during the talks in the Swiss city.
"The talks on implementing the accord are not easy. They are progressing, but slowly," he said.
"I hope all sides will avoid delving into issues that could become troublesome and complicate the process," Zarif added, without elaborating.
Bonino arrived Saturday in Tehran, on a rare visit to Iran by a senior European official.
Iranian chief negotiator Abbas Araqchi earlier told ISNA that Zarif would talk to Ashton over "serious differences" on how to implement the nuclear deal.
Neither Araqchi nor Zarif gave any other details.
Nearly a month ago in Geneva, Iran and world powers reached a deal that is meant to buy time for a diplomatic solution to a decade-long stand-off over Tehran's disputed nuclear ambitions.
Under the accord, Iran agreed to roll back or freeze parts of its nuclear drive for six months in exchange for modest sanctions relief and a promise by Western powers not to impose new sanctions.
Western powers suspect Iran's nuclear activities mask military objectives, despite repeated denials in Tehran that they are entirely peaceful.