WASHINGTON, Sept 3: The International Atomic Energy Commission has evidence that Pakistan supplied Iran critical technology and parts for gas centrifuges that can be used to enrich uranium, the Washington Post reported on Wednesday.

Pakistan has denied providing such assistance but the paper says that Pakistan is one of only a handful of countries that remain outside the nuclear Non-Proliferation Treaty. As such Pakistan technically is not bound by many of the international restrictions on the export of nuclear technology, the report says.

The Post says the possibility that Pakistan could be implicated in Iran’s nuclear programme presents a diplomatic challenge to the Bush administration, which has been reluctant to publicly criticize Pakistan because it has provided crucial assistance in the US campaign in Afghanistan.

“The notion that Pakistan wasn’t involved is getting less and less tenable,” Henry D. Sokolski, a top nonproliferation official in the Pentagon in the George H.W. Bush administration, told the Post. “Some might make the claim that this was something that happened in the past. But it wasn’t all that long ago.”

The Bush administration declined to comment on the IAEA’s findings, but it continued to express skepticism about the veracity of Iran’s nuclear claims.

“They have clearly not been forthcoming in the past with the actual facts and details about their secret nuclear programmes, and that’s what’s been of great concern to us,” said the State Department’s deputy spokesman, Philip Reeker.

The report says that Iran has admitted for the first time that it received substantial foreign help in building a secret nuclear facility south of Tehran that is now beginning to enrich uranium.

While Iran has not yet identified the source of the foreign help, evidence collected in Iran by the UN nuclear watchdog agency implicates Pakistani companies as suppliers of critical technology and parts, officials familiar with a UN investigation of Iran’s programme told the paper. Pakistan is believed by many proliferation experts to have passed important nuclear secrets to both Iran and North Korea, the report says.