Talks between Iran and world powers aimed at finalising a deal over Tehran's nuclear programme could go beyond a June 30 deadline, a senior Iranian negotiator said.

"We are not at the point where we can say that negotiations will be completed quickly -- they will continue until the deadline and could continue beyond that," Abbas Araghchi was quoted as saying by the official IRNA news agency.

Araghchi was attending a fresh round of talks between Iranian representatives and officials from the P5+1 group of nations, which got under way in Vienna on Tuesday.