Iran has blocked UN nuclear inspectors from visiting a key underground site as the international community calls for it to cease sensitive atomic fuel work, diplomats said on Tuesday.
The diplomats said the Iranian authorities are making life increasingly difficult for inspectors from International Atomic Energy Agency but that the UN watchdog is still able to monitor the country's nuclear programme.
As well as blocking a visit to a uranium enrichment facility under construction, Iran has refused visas for a few inspectors and is giving mainly short-term, one-entry visas instead of longer-term, multiple-entry visas.
The problems emerged as Iran delivered its response to a call by six world powers to suspend uranium enrichment, the process that makes nuclear power reactor fuel but also raw material for atom bombs. If Iran refuses, UN sanctions could follow.
They are not yet "deemed to be systematic and obstructionist," said a diplomat close to the IAEA who asked not to be named due to the sensitivity of the issue.
If they were, the diplomat said, the IAEA board of governors would be required to act on violations of the nuclear Non-Proliferation Treaty (NPT).
The diplomat said IAEA inspectors had been turned away over the weekend from an underground plant under construction at a uranium enrichment facility in Natanz in central Iran.
There are no centrifuges yet installed at this site, the diplomat said, referring to the machines, which enrich uranium.
Iran is running centrifuges at a pilot enrichment plant above ground at Natanz.