A senior negotiator said Iranian and US delegations held "detailed" discussions on Tehran's uranium enrichment program and sanctions in their nuclear talks in Zurich, Switzerland on Friday and Saturday.
Abbas Araqchi told reporters on Sunday that due to the complex nature of the talks, a speedy resolution is impossible; however, both sides are "serious" about their effort to narrow the remaining differences.
He said bilateral and trilateral meetings with the US delegation and European Union political director Helga Schmid were held, adding that Iran and US delegations also held expert-level talks.
Deputy Foreign Ministers Araqchi and Majid Takht-Ravanchi met with US Under Secretary of State for Political Affairs Wendy Sherman, who was heading the US delegation.
"In these meetings, we entered into discussions on different subjects, especially important subjects such as enrichment and sanctions, which have exhaustive and complicated details," Araqchi noted.
The future size and scope of Iran's uranium enrichment program and the speed of ending sanctions have been among major sticking points in the talks and Tehran has always stressed that it will not accept any "excessive demands" in relation to these issues.
The deputy foreign ministers of Iran, Britain, France and Germany are set to hold talks over Tehran's nuclear program on January 29 in Istanbul, Turkey.
Araqchi added that representatives from China and Russia may join the talks in Istanbul.
