Farooq Muhammad, director of Pakistan's key uranium enrichment facility Kahuta Research Laboratories (KRL), and a KRL laboratory director, Yasin Chohan, were arrested this month, the reports said.

"They have been arrested and are under detention," opposition senator Ishaq Dar, of the Pakistan Muslim League-Nawaz (PML-N) party, told AFP.

"I say this with full responsibility on the basis of credible information."

Local Urdu-language newspaper Jinnah reported that caucasian men wearing bullet-proof jackets had arrested Farooq at his home in Rawalpindi, near Islamabad. It said Chohan was also taken from his home.

A government spokesman refused to confirm whether the two men were in detention, saying only that nuclear scientists routinely underwent "personnel dependability and debriefing programs".

A foreign ministry statement added "the matter referred to falls within the scope of such programs".

The government rejected local media reports that the two men were connected to alleged transfers of nuclear technology to Iran.

"There are reports about many sources from where Iran could have obtained nuclear technology, including several Western companies and individuals. The focus should be on checking out with those sources," the foreign ministry said.

The PML-N party said it believed the two men were being held by US Federal Bureau of Investigation (FBI) agents.

"According to our information, the FBI is holding Director General Dr Farooq and Laboratory Director Yasin Chohan with the assistance of Pakistani agencies," said a party statement, condemning the arrests.

It raised concerns that the architect of Pakistan's nuclear program, Abdul Qadeer Khan, may also have been arrested.

Khan, who founded KRL, has been named in international media reports, quoting foreign intelligence officials, which claim that Pakistan aided both Iran's and North Korea's nuclear program.

KRL, based on the outskirts of Pakistan's capital Islamabad, was sanctioned by the United States in March for allegedly helping an unnamed foreign country or entity to develop weapons of mass destruction.

Islamabad, which went public as a nuclear power in May 1998 when it conducted underground nuclear tests, consistently denies reports of exporting nuclear know-how.

WAR.WIRE