The dispute has further strained ties between Iran and the International Atomic Energy Agency (IAEA) and deepened concern about Iran’s nuclear program, which the West suspects is designed to develop atomic weapons.

IAEA Director-General Yukiya Amano said earlier this week Iran’s refusal to admit some experienced inspectors was hampering the agency’s work.

Iran, which says its nuclear program is aimed at generating electricity, said two inspectors it banned in June had provided false information about its activities.

It says it is its right to refuse inspectors under its non-proliferation accord with the UN body and the agency has a pool of more than 150 other experts it can use. The US envoy to the IAEA told a closed-door meeting of the agency’s 35-country board that Iran was making a “clear effort” to intimidate inspectors and influence their work.

“It is unprecedented for a state to reject inspectors because they report accurately... what they see and hear,” US ambassador Glyn Davies said according to a copy of his speech.

In a separate statement at the meeting, France, Germany and Britain voiced concern about what they called Iran’s growing failure to cooperate with the UN body.

“Iran’s refusal to fully cooperate with the IAEA and its deliberate attempts to prevent it from carrying out its mandate in Iranian territory are ... troubling and reprehensible,” the statement read out by France said. “The Iranian authorities are clearly attempting to intimidate the agency so as to influence its ability to report to the board and undermine its ability to effectively implement the safeguards regime in its territory,” it said.

Besides those barred in June, Tehran cancelled access for a senior Middle East inspector in 2006 and has objected to several other designated inspectors in the past.

If Iran continues to refuse inspectors it could face diplomatic consequences at the IAEA, whose governors referred Iran’s dossier to the UN Security Council in 2006 over its nuclear secrecy and lack of full cooperation.

Davies referred to language in the IAEA’s agreements with member states governing inspections, which he said “indicates that the board should consider ‘appropriate action’ when inspections are being impeded” by the rejection of inspectors.

Amano’s latest report on Iran showed it was pushing ahead with its nuclear work despite tougher sanctions imposed by the United Nations, the United States and the European Union.

It expressed growing frustration over what the IAEA sees as Iran’s failure to respond to concerns about possible military dimensions to its activities.

The EU trio said Iran seemed “determined to pursue a nuclear program which could provide it with military capabilities”.

Relations between Iran and the IAEA have deteriorated since Amano took over as head of the agency in December.

He has taken a firmer approach on Iran than his predecessor Mohamed El-Baradei, saying in reports to the board that Tehran could be trying to develop a nuclear-armed missile.

Iran has accused Amano of issuing misleading and politicized reports about its nuclear program. The head of Iran’s Atomic Energy Organization, Ali Akbar Salehi, hit back at Amano on Tuesday, suggesting he had made a dangerous mistake by criticizing Iran for its rejection of inspectors.