Iran negotiator Ali Larijani has given no specifics on what he will be bringing to Friday's talks, which are to be held in Vienna and come ahead of a meeting next week of the UN nuclear watchdog to assess Iran's nuclear program.
"There is no pre-declaration" for Friday's meeting, the diplomat said.
The surprise meeting was requested by Iran, which has been trying to strike a compromise with Russia to resolve the impasse over its nuclear program, which the United States claims hides secret development of atomic weapons.
The watchddog International Atomic Energy Agency's 35-nation board of governors had in February reported Iran to the UN Security Council, which is waiting for the Vienna-based IAEA's assessment before deciding what measures to take on Iran's nuclear program.
But there seemed to be little room for compromise, with Iran insisting on its right to enrich uranium.
At the same time the European Union and the United States insist that Tehran must give up this process, which makes nuclear reactor fuel but also atom bomb material.
The European trio which negotiates for the EU on Iran has warned Tehran in writing that progress Friday is totally dependent on Iran stopping uranium
enrichment and cooperating with UN nuclear inspections.
But an Iranian diplomat told AFP there "could be a breakthrough if things
go well" and that the meeting "could be a good opportunity to reach a general
understanding that could defuse the situation."
The talks come ahead of a crunch meeting March 6 of the United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA).
The IAEA is to make an assessment of Iran's nuclear program that will be sent to the UN Security Council, which could then take punitive action.