Iran and six world powers entered detailed negotiations Tuesday, aiming to find a long-term solution to Tehran's nuclear program.

The third round of talks between Iran and five UN Security Council permanent members - Britain, China, France, Russia, the United States - plus Germany, is a bid to draft a comprehensive agreement that will allow Iran to continue its nuclear development program while reassuring the powers it will not be used for military purposes.

"They are doing detailed work on issues," said Michael Mann, spokesperson of EU foreign policy chief Catherine Ashton, noting the atmosphere of the meeting was good so far.

Both US and Iranian officials have voiced the hope of starting the drafting of an agreement in May.

The detailed discussions are based on a six-month interim deal reached in Geneva last December.

Iranian Foreign Minister Mohammad Javad Zarif, the chief Iranian negotiator in the talk, said the six months' time is adequate for discussion to make a comprehensive agreement on the Iranian nuclear program, if sides involved come with "good faith and will," after his meeting with Ashton Monday evening in Vienna.

The West has long suspected Iran is developing nuclear weapons under the cover of a civilian atomic plan, while Tehran says its nuclear program is solely peaceful.