Araqchi, speaking to reporters at the end of all-day closed-door talks, said there was an agreement to continue nuclear talks "next month" at a venue to be decided.
"We had very intense negotiations. It was very useful and helpful," Araqchi said, without giving details.
The U.S. negotiating team led by Acting Deputy Secretary of State Wendy Sherman left the meeting, held at the European Union's diplomatic mission, without making any comment.
A EU spokeswoman said no statement would be issued on Wednesday following the talks, attended by EU political director Helga Schmid.
Earlier on Wednesday, Iranian Foreign Minister Mohammad Javad Zarif said nuclear talks with major powers were being conducted in a good atmosphere, "good steps" had been taken and more would follow.
U.S. and Iranian negotiators held a two-day meeting on Monday and Tuesday in the Swiss city which paves the way for wider talks on how to end the 12-year dispute over Tehran's nuclear programme.
On Monday, Iran's official IRNA Iran's official IRNA quoted an unnamed member of Tehran's delegation as saying uranium enrichment and how to remove sanctions were sticking points in the bilateral talks.