Six world powers started nuclear talks with Iran on Friday.

European Union foreign policy chief Catherine Ashton heads the delegations representing six big powers -- Britain, China, France, Germany, Russia and the United States.

Iran is represented by its nuclear negotiator Saeed Jalili.

There is no media access to the venue of the crucial nuclear talks in Istanbul since police maintains high level of security.

Six world powers try to persuade Iran to rein in its nuclear program at talks with expectation of some breakthrough.

Some diplomats are hopeful that the two-day talks in Istanbul will be more fruitful than a similar gathering in Geneva last month.

Chinese Assistant Foreign Minister Wu Hailong told Xinhua before the start of talks, "I believe that we can achieve some progress if all relevant parties show some kind of flexibility in the talks."

This week's round of nuclear meetings with Iran in Istanbul is hope to help foster dialogue, in spite of an increasingly defiant Tehran calling the talks a 'last chance for the West.'

The talks take place just over a month after the last such meetings, held in Geneva in early December.

The December talks, while significant for resuming dialogue between Iran and world powers after a 14-month hiatus, achieved little more than an agreement to hold another round of talks in Istanbul.