Iran's new chief nuclear negotiator is to meet EU envoy Javier Solana in Rome as diplomats try to detect any hardening in Tehran's policy.
Saeed Jalili has a reputation in Iran of being a hard-liner
The talks will be the first with the EU since Saeed Jalili, a close ally of President Mahmoud Ahmadinejad, took over from Ali Larijani.
Mr Larijani quit amid differences with President Ahmadinejad over how to proceed with negotiations.
However, he is due to accompany his successor to the Rome meeting.
The deputy speaker of the Iranian parliament has said that Mr Larijani resigned because he could no longer work with Mr Ahmadinejad, confirming suspicions that they had fallen out on policy, and possibly personality as well.
Born in 1965
Is close to President Ahmadinejad
Considered a hard-line diplomat
Appointed deputy foreign minister in charge of Europe and American affairs in 2005
Has worked in supreme leader's office
But he will still be in Rome for the talks as the representative of Iran's supreme leader, Ayatollah Ali Khamenei.
The talks are due to begin in the afternoon at the Italian city's lavish Doria Pamfili villa, Reuters news agency reports.
One of Ayatollah Khamenei's top advisers said Mr Larijani should not have been allowed to resign.
It is once more sign of deep divisions within the Iranian government about their tactics in the nuclear dispute, the BBC's Jon Leyne reports from Tehran.
The UN Security Council is waiting for reports from Mr Solana and from its nuclear watchdog, the IAEA, before deciding on a third round of tougher sanctions against Iran.
Iran is developing the technology to enrich uranium on an industrial scale. The enriched uranium can be used as fuel in a nuclear power station.
Some Western countries, led by the US, fear Iran will further process the enriched uranium for use in nuclear weapons.
The IAEA says there are outstanding questions about Iran's nuclear activities but that it has recently reached agreement with Tehran on a "work plan" to resolve those issues.