The International Atomic Energy Agency (IAEA) team was due to return to Vienna on Friday morning, the source said, following the talks aimed at finding a solution to concerns over Iran's nuclear program.
The West suspects it is aimed at developing a nuclear weapons capability.
This comes as Russia said on Thursday it’s trying to firm up plans for a new round of talks this month between global powers and Iran.
Iranian news agency ISNA said on Wednesday that Iran and six world powers would resume talks in late January, but a European Union official claims the two sides had yet to agree a date and venue.
The Russian Foreign Ministry said later that there was an understanding among the parties involved that the meeting should take place later this month, reported by ISNA.
World powers are watching the IAEA-Iran meeting for any signs as to whether Tehran, which faces intensifying sanctions pressure, may be prepared to finally start tackling international concerns about its nuclear activity.
Western and Russian diplomats had hoped for talks to restart in December or mid-January. Since the last meeting in June, Iran has pressed ahead with disputed nuclear activity and amassed more material that can have both civilian and military purposes.
Russia approved four rounds of U.N. Security Council sanctions against Iran over its nuclear program but opposes new curbs and has called separate Western sanctions counterproductive.
Russia has warned that an Israeli attack on Iranian nuclear facilities would be disastrous and, while Moscow says Tehran must dispel concerns about its nuclear program, it has suggested Western fears about military aims are overblown.