World powers are hoping in crunch talks in Baghdad on Wednesday to persuade Iran to suspend sensitive nuclear work in order to ease fears that Tehran wants the bomb and to abate Middle East tensions.
Iran, however, is expected to press the P5+1 - the US, Russia, China, Britain, France and Germany - to ease sanctions and accept its right to a peaceful nuclear programme. It denies wanting atomic weapons.
Iran's lead negotiator Saeed Jalili was quoted by Iranian media as saying he hoped the talks would be the start of a "new era" in relations.
The West fears that a nuclear-armed Iran would destabilise the already volatile Middle East and sound the death knell for 60 years of international efforts to prevent the spread of atomic weapons, sparking a regional arms race.
Israel, Washington's closest ally in the region, feels its very existence would be under threat and has refused to rule out a pre-emptive strike on Iran's nuclear facilities.
United States President Barack Obama, seeking re-election in November against a Republican challenger accusing him of dawdling over Iran and keen to see oil prices come down, is impatient for results, while Iran is feeling the pinch from the sanctions.