Vienna, July 2 (IANS): Iran and six world powers are making progress in the latest round of talks over Iran's long-disputed nuclear programme, said top diplomats of the US and Iran here.

"We have some very difficult issues, but we believe we are making progress and we are going to continue to work because of that," said US Secretary of State John Kerry after a meeting with Iranian Foreign Minister Mohammad Javad Zarif in Vienna here on Wednesday, one day after the self-imposed June 30 deadline.

Earlier on Wednesday, Zarif also told reporters: "We have made progress and we will make progress and we will use every opportunity to make progress."

French Foreign Minister Laurent Fabius and his Chinese counterpart Wang Yi were expected to join the negotiations in Vienna on Thursday, along with European Union foreign policy chief Federica Mogherini, Xinhua news agency reported.

As US State Department deputy spokeswoman Marie Harf announced on Tuesday, the fresh round of nuclear talks was extended from June 30 to July 7.

Iran and the P5 1 group -- the US, Britain, France, Russia, China, plus Germany -- agreed on a framework of understanding in April, and set June 30 as the deadline for concluding a final deal, after missing two previous deadlines in June and November.