By Kerry Skyring
BBC News, Vienna
Top Iranian negotiator Ali Larijani is due to hold to talks in Vienna with the head of the UN nuclear watchdog agency, Mohamed ElBaradei.
Iran says its nuclear programme is for peaceful purposes only
The talks come as permanent members of the Security Council consider tougher sanctions against Tehran over its refusal to give up uranium enrichment.
Iran insists the meeting is not about making concessions.
Iran's ambassador to the International Atomic Energy Agency (IAEA) said suspension was "out of the question".
He said the meeting will be about strengthening co-operation between the IAEA and Iran.
That could include clearing up unresolved questions about some of Iran's past nuclear activities.
Iran says it wants to do that but UN nuclear inspectors complain they have been stonewalled.
After the Vienna meeting, Mr Larijani goes to Lisbon for talks with the EU's foreign policy chief, Javier Solana.
It was at a previous meeting with Mr Solana that Mr Larijani said Iran was ready to do more to answer questions about its past nuclear activities.
But almost a month later, there is no sign of progress.