Iran and six world powers began a new round of talks on Tuesday aimed at settling the dispute over Tehran's nuclear program by late July, despite wide differences on how to attain that goal.

The powers want Iran to scale back its uranium enrichment activity to deny it any capability to quickly produce an atomic bomb, if it decided on such a course. Iran says its nuclear program is entirely peaceful and wants them to lift sanctions.

Chief negotiators from Iran, the US, the UK, France, Germany, Russia and China started a two-day meeting on Tuesday at the UN complex in Vienna, where they have held two previous such sessions since February.

"We are involved in very detailed and substantial negotiations and we are trying as hard as we can to drive the process forward," the spokesman for European Union foreign policy chief Catherine Ashton, who coordinates the discussions on behalf of the powers, told reporters.

Both sides say they want to start drafting a comprehensive agreement in May, two months before a July 20 deadline for finalizing the accord. Western officials say, however, that the parties are far apart on key issues.

Iranian and US negotiators are wary that any deal will face criticism from conservative hardliners at home wedded to confrontation since Iran's 1979 Islamic Revolution.

The six nations have agreed internally to have a draft text of an accord by the end of May or early June, one diplomat from the powers said, adding however, "We're still in an exploratory phase ... In the end, things will happen in July."

Tuesday's opening session was chaired by Ashton and Iran Foreign Minister Mohammad Javad Zarif, but their deputies later took over.

The Islamic Republic says its enrichment program is a peaceful bid to generate electricity and has ruled out shutting any of its nuclear facilities.

The US and some other Western countries have accused it of working on developing a nuclear bomb capability. Israel has threatened to attack its long-time foe Iran if diplomatic efforts fail.

Iran says it is Israel's assumed atomic arsenal that threatens peace and stability in the Middle East.

The diplomat said issues to be discussed at the meeting included how the UN nuclear watchdog would verify whether Iran was meeting its end of any deal, suspected past atomic bomb research by Tehran, and how to deal with UN Security Council resolutions on Iran adopted since 2006.

Reuters