Chinese Foreign Minister Wang Yi is in Vienna to join the talks on the Iran nuclear issue.
Negotiators are trying to reach a final deal which would curtail Iran's nuclear program in exchange for relief from economic sanctions.
Wang Yi says he is optimistic about a deal but cautions there are still difficult issues to resolve.
"I think there is a high possibility for a deal, but I still need to consult with my colleagues. The nuclear talks have entered a fast period; however, we are still faced with many important and sensitive issues that cannot be avoided. China has come here to help resolve the issue and we will bring some solutions and thoughts."
Wang Yi expects a fair, balanced and just solution at the talks.
On Tuesday, Iran and representatives from the five permanent members of the UN Security Council, plus Germany, missed a self-imposed deadline to reach a final agreement, but did agree to extend the deadline to July 7th.
Major sticking points include the pace and timing of sanctions relief, and the monitoring and verification of Iran's nuclear program.
French Foreign Minister Laurent Fabius is also joining the Vienna talks.
"There are things that have moved forward but the negotiations have not ended yet. There will be more work done by our collaborators and I expect to come back to Vienna Sunday night. And I hope that then, we will be able to move forward, to, maybe, let's hope for it, a final solution which would allow for a robust deal."
Meanwhile, the head of the International Atomic Energy Agency is in Tehran to discuss with Iranian officials methods for clarifying key nuclear issues.
Yukiya Amano has met President Hassan Rouhani and other senior officials.
The two sides have reportedly reached an agreement on the timetable for cooperation to solve existing problems.
Tehran has been reluctant to allow UN inspectors access to its military sites and nuclear scientists to verify if Iran's nuclear program has any military purposes.
