EU foreign policy chief Catherine Ashton's spokesman Michael Mann tweeted that the first plenary session of P5+1 and Iran nuclear talks has ended, which now continue in bilateral format.
At the same time Iran's Tasnim news agency reported that Iran and China are currently holding the bilateral negotiations.
Iran and the P5+1 reached a nuclear agreement on Nov. 24. Iran has agreed to curb some of its nuclear activities for six months in return for sanctions relief. Both Iran and the P5+1 group have agreed to implement the agreement starting from Jan. 20.
Under the agreement, six major powers agreed to give Iran access to $4.2 billion in revenues blocked overseas if it carries out the deal, which offers sanctions relief in exchange for steps to curb the Iranian nuclear program.
The U.S. and its Western allies suspect Iran of developing a nuclear weapon - something that Iran denies.
The Islamic Republic has on numerous occasions stated that it does not seek to develop nuclear weapons, using nuclear energy for medical researches instead.