The deadline to reach a long-term comprehensive deal on the Iranian nuclear issue was extended last month from June 30 to July 7 in Vienna. The world has never been so close to resolving the Iranian nuclear issue, as US Secretary of State John Kerry said on Monday, but a number of unresolved issues could still let this hard-won opportunity slip, which would be a shame.

Before the latest round of talks began, Foreign Minister Wang Yi was optimistic about the outcome and reiterated that China has played a constructive role in the marathon negotiations over the past 16 months.

After the ice-breaking telephone conversation between US President Barack Obama and Iranian President Hassan Rouhani in September, 2013, Iran and P5+1 - the five permanent UN Security Council members, the United States, Britain, France, Russia and China plus Germany - have been engaged in on-and-off talks. After agreeing on a framework of understanding in April, they set June 30 as the deadline for reaching a final deal, which was later deferred to July 7. And during earlier talks, Iran agreed to suspend some sensitive nuclear activities while Western countries promised to lift part of the sanctions on Teheran.