IAEA demands Iran nuclear access to Parchin site
The chief of the United Nations nuclear watchdog has called for access to Iran's Parchin military site "without further delay" and without waiting for negotiations to make progress.
The International Atomic Energy Agency (IAEA) has long suspected nuclear weapons research is taking place at the site, just outside Tehran.
It has not had access to the military complex since 2005.
Tehran says it is refining uranium only for peaceful energy purposes.
Director general Yukiya Amano made the comments in a speech to the IAEA's governing board.
"Providing access to the Parchin site would be a positive step which would help to demonstrate Iran's willingness to engage with the agency on the substance of our concerns," he said.
Access should be granted without waiting for further talks, Mr Amano added.
The IAEA suspects Iran could have carried out experiments with explosives capable of triggering a nuclear weapon at Parchin.
The UN agency has been trying to encourage Iran to cooperate with its investigations into suspected nuclear weapons research for more than a year, but Mr Amano admitted he was "unable to report any progress".
Last month he sent a delegation to Tehran in the latest of a series of talks to negotiate a possible resumption of site visits, but the head of Iran's atomic energy programme Fereydun Abbasi-Davani said visits to Parchin or any other site were "not on the agenda".
Mr Amano said he remained committed to negotiations, but warned they must proceed with "a sense of urgency and a focus on achieving concrete results".
Iran is also continuing separate talks with the five members of the UN Security Council - the UK, US, France, Russia and China - as well as Germany.
The last round was held in Kazakhstan last week. They were described as "useful" by a Western diplomat, but there appears to have been little progress on the central issue of Iran's uranium enrichment programme.
Earlier in February Iran also said it was installing upgraded uranium enrichment centrifuges at a separate research site - a move the US described as "an escalation".
Iran denies that it is trying to develop nuclear weapons, arguing that it is entitled to develop a civilian nuclear energy generation programme under the international nuclear Non-Proliferation Treaty, of which it is a signatory.
Last week it announced it had found large new uranium deposits, trebling the size of its uranium supply, and was planning to expand its nuclear power programme.