BRUSSELS - Foreign ministers and the chief negotiator for world powers will meet next week to try to figure out how to break an impasse in negotiations over Iran's nuclear program, after talks on Tuesday yielded no sign of progress.

Six world powers, represented by European Union foreign policy chief Catherine Ashton, have sought to persuade Iran to scale back its nuclear program through intensifying economic sanctions and diplomacy.

In the latest talks, Ashton and Iran's chief negotiator Saeed Jalili held a meeting in Istanbul that was described as "useful and constructive".

It was "an important opportunity to stress once again to Iran the urgent need to make progress," according to Ashton's spokesman.

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