Iran has banned a senior UN nuclear inspector who has criticised the Tehran government from visiting the country, a Western diplomat said on Sunday.

The diplomat, who spoke on condition on anonymity, was confirming a report in the German newspaper Welt am Sonntag, in which International Atomic Energy Agency (IAEA) Iran section head, Chris Charlier of Belgium, was reported as saying that he had not been allowed into Iran for several months.

"I haven't been allowed to travel to Iran since April," he was quoted as saying. "Since April, I have had no more contact with the Iranian nuclear file."

But a senior diplomat at the Vienna-based IAEA said Charlier was still the chief of the agency's Iran section.

The IAEA has been inspecting Iran's nuclear programme since 2003. Although it has found no hard evidence that Iran is working on atomic weapons, it has uncovered many previously concealed activities linked to uranium enrichment, a process of purifying fuel for nuclear power plants or weapons.

Tehran denies pursuing atomic weapons but refuses to temporarily halt its enrichment programme as demanded by Germany and the five permanent members of the U.N. Security Council.

Charlier was also quoted as saying he believed Iran was probably still hiding things from the IAEA.

"It is very probable that Tehran is doing things in the nuclear field that to this day we have no clue about," he said.

It was not immediately clear why Charlier was banned from Iran. But last year he was interviewed for a BBC documentary on Iran's nuclear programme and complained about the lack of freedom U.N. inspectors face in the country.

"Whatever we say, whatever we do, they're always behind us with a video camera, with a microphone trying to record all our movement and all things that we're saying," Charlier said, according to a transcript of the programme published on the Internet.