UN experts left Tehran empty-handed today after trying to get Iranian officials let them restart an investigation into claims the country is making nuclear weapons.
International Atomic Energy Agency (IAEA) deputy director Herman Nackaerts said there would be more talks on February 12.
But any progress made then will be too late for the meeting between Iran and the P5+1 - the US, Russia, China, Britain, France and Germany - slated for the end of January.
Those nations had hoped that the Iranians would show a readiness to compromise at the IAEA meeting, leading to Iran agreeing to stop enriching uranium that could be used in a bomb.
Iran has repeatedly said such a deal is irrelevant as it is only using the enriched uranium for nuclear reactor fuel and scientific and medical purposes.
In addition, Supreme Leader Ayatollah Ali Khamenei issued a fatwa in 2005 that banned nuclear weapons.
Iran has stopped answering questions about alleged secret weapons research that took place more than four years ago, saying it has provided enough evidence to disprove such claims.
New attempts to restart the investigation have dragged on for more than a year, with Tehran insisting on a detailed outline of what IAEA experts may or may not do.
The IAEA suspects that Iran has conducted live tests of conventional explosives at the Parchin site south-east of Tehran.
The agency already visited Parchin twice, the last time in 2005.
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