The talks between six world powers and Iran over Tehran's nuclear issue achieved positive achievements, a Chinese government official said here Saturday after a seven-hour meeting between the parties.

China's Assistant Foreign Minister Ma Zhaoxu, who is also Beijing's representative to the renewed talks on Iran's disputed nuclear program, said in a statement after the meeting that this round of dialogue is serious, useful and constructive.

The talks between Iran and the UN Security Council's five permanent members plus Germany, known as P5+1, were held at Istanbul Convention Center on Saturday -- about 15 months after the last round of negotiations, which were also held in Istanbul, turned out fruitless.

"We exchanged views on the Iranian nuclear issue. All sides are willing to conduct dialogue and negotiation based on the principle of step by step and reciprocity as well as on the basis of equality and mutual benefit so as to build mutual trust for the comprehensive, just and proper settlement of the Iranian nuclear issue," Ma said after Saturday's talks.

"Thanks to the efforts of all sides, today's meeting starts a sustained process of dialogue and has made positive achievements," he said.

Ma said that China has made unremitting efforts for the resumption of the dialogue. "Prior to the meeting, we have kept frequent contacts with all sides, urging for diplomatic solution and early resumption of the negotiations," he said.

During the talks, "we pushed all sides, in the spirit of forward-looking, to show flexibility and sincerity, and take each other's concerns seriously so as to make the dialogue a success," said the Chinese official.

Ma meanwhile noted that the Iranian nuclear issue is a complicated one, stressing "We may encounter difficulties or setbacks of all kinds in the future."

"We hope all parties ... could cooperate with sincerity ... and make greater efforts for the peaceful settlement of the Iranian nuclear issue through dialogue and negotiation," he said.

China stands ready to work with all sides to promote talks and peace, and will continue to play a constructive role in the settlement of the Iranian nuclear issue through peaceful dialogue, he added.

Shortly after the talks, European Union's foreign policy chief Catherine Ashton, who headed the delegations of the six world powers, also described as "constructive and useful" the Istanbul talks.

She also said that they will meet again in Baghdad of Iraq on May 23 this year.