The talks are aimed at resolving a dispute over Iran's nuclear programme, which world powers fear is masking a weapons drive but which Tehran insists is entirely for peaceful purposes.
"January 21 and 22... the 1st and 2nd of (Persian month of) Bahman ... has been agreed by the two parties," foreign ministry spokesman Ramin Mehmanparast told reporters.
Turkish Foreign Minister Ahmet Davutoglu had confirmed the two dates on Saturday.
European Union foreign policy chief Catherine Ashton, who represents the six world powers -- Britain, China, France, Russia, the United States and Germany -- in the talks, had suggested 20 January for the resumption of negotiations.
The previous round of talks took place in Geneva on 6 and 7 December, ending a 14-month hiatus in negotiations focused on Iran's uranium enrichment programme.
Iran's nuclear programme has grown under the presidency of Mahmoud Ahmadinejad, attracting four rounds of UN sanctions and other unilateral punitive measures from various countries, including the United States.