Iran's outgoing nuclear negotiator, Ali Larijani, is to accompany his successor to scheduled talks with the European Union in Rome on Tuesday.
Mr Larijani has led negotiations with the West
President Mahmoud Ahmadinejad accepted Mr Larijani's resignation on Saturday. Saeed Jalili was appointed to the post.
Mr Larijani had differences with the president over how to proceed with negotiations, correspondents say.
Western countries suspect Iran of trying to build nuclear weapons but Tehran says its programme is peaceful.
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
Mr Larijani has favoured further negotiations with the West over Iran's uranium enrichment programme, as opposed to the president's more hard-line approach, the BBC's Jon Leyne, in Tehran says.
Iranian foreign ministry spokesman Mohammad Ali Hosseini told a news conference in Tehran that Dr Larijani would be at the Rome talks as the representative of Supreme Leader Ayatollah Ali Khamenei.
The UN Security Council is waiting for reports from the EU's Javier Solana and from the UN's 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.