"We call on Iran to supply all the necessary information, as well as the access to people, documents and sites requested by the IAEA," or International Atomic Energy Agency, French ambassador Francois-Xavier Deniau told the agency's 35-member board at its meeting here.
He was speaking on behalf of the so-called EU-3 comprising Britain, France and Germany.
"That is the only way for the agency to determine the true nature of the Iranian nuclear programme," he said in a speech, a copy of which was obtained by AFP.
The Slovenian representative to the IAEA, Bojan Bertoncelj, whose country currently holds the rotating EU presidency, echoed the French envoy.
The EU "remains seriously concerned that despite more than five years of intense efforts by the IAEA, the agency is still not in a position to determine the full nature of Iran's nuclear programme," Bertoncelj said.
IAEA chief Mohamed ElBaradei in his latest report had accused Iran of withholding key information that could shed light on the so-called alleged studies including research, engineering work and testing with a possibly military dimension.
The allegations have been backed up by intelligence from 10 different countries. But Iran has simply dismissed the intelligence as "fake" and "fabricated".
"A simple rejection by Iran of this information as not authentic, forged or fabricated is neither credible nor acceptable, given the quality and quantity of the documents," Bertoncelj said.
"In this regard, the EU notes with concern that the agency is of the view that Iran may have additional information, in particular on high explosives testing and missile related activities, which could shed more light on these important questions and which Iran should share with the agency," he said.
While the debate about Iran has dominated the board meeting this week, another equally contentious issue has also been looming large — allegations that Syria had built a clandestine nuclear raactor until it was bombed by Israeli airplanes last September.
IAEA chief ElBaradei announced on Monday that a team of UN inspectors will travel to Syria June 22-24.
The US ambassador to the IAEA, Gregory Schulte, said it was "imperative that Syria fully cooperate with the IAEA and in no way hinder the investigation either by further delaying an inspection or by refusing the IAEA unfettered access to any site requested by the IAEA."
A diplomat, speaking on condition of anonymity, told AFP that Syria had informed other Arab League countries on the sidelines of the IAEA meeting that Damascus had agreed to let the experts inspect the bombed building itself in Al-Kabir — a remote site in the Syrian desert.
But no other sites had been specified, the diplomat said, despite US media reports claiming the IAEA was also keen to visit two or three other suspect locations.
In April, the United States turned over intelligence alleging the building was an undeclared nuclear reactor, close to completion, but not yet supplied with the necessary nuclear material.
Damascus has dismissed the accusations as "ridiculous".
However, it wiped the destroyed site clean of rubble late last year and erected a new building where the destroyed one had stood, making any possible investigation by the IAEA more difficult.
In comments to newspapers in the United Arab Emirates on Tuesday, Syrian President Bashar al-Assad again strongly denied the allegations.
"If anyone had a secret dossier on nuclear facilities in Syria with a Korean role, as they claim, then why did they wait for seven months before destroying a normal military facility by the Israeli raid?" al-Assad said in comments reported by the Gulf News.
