Chinese vice Foreign Minister Li Baodong told reporters on Sunday in Vienna there won't be a long extension of Iranian nuclear negotiation, and that a comprehensive deal could be possible within one week.

Chinese Vice Foreign Minister Li Baodong (2nd L) meets with Iranian Foreign Minister Mohammad Javad Zarif (3rd R) in Vienna, Austria, June 28, 2015.

Sides are only "a step away" from the comprehensive Iranian nuclear deal though many tough issues still needed to be resolved, Li added.

It is clear that there is little chance to strike a deal before the self-imposed June 30 deadline, as some gaps remain and a lot of work still needed to be done.

Iran and five UN Security Council permanent members plus Germany have been negotiating over the past 14 months to reach a long-term deal over Tehran's disputed atomic plan. During the period, Iran would suspend some sensitive nuclear activates, in return, western states would partially relieve some sanction imposed on Tehran.