Two scientists at Pakistan's top nuclear laboratory have been taken into custody for questioning, Pakistani sources said Thursday.

The nuclear scientists at the Khan Research Laboratories (search) were being interrogated after complaints were made against them, a government official and two Pakistanis affiliated with the country's nuclear programs said. All three spoke on condition of anonymity.

Confirming reports in three Pakistani newspapers Thursday, the sources identified the two detained men as Yasin Chohan and Mohammad Farooq, the former director general at the laboratories. Farooq also is a former aid to the founder of Pakistan's nuclear weapons program, Abdul Qadeer Khan (search), who had the research laboratories named after him.

The sources declined to describe the complaints that were made against Chohan and Farooq, or where they originated. They also denied a story in the Lahore-based Nation newspaper Thursday saying that the two men were being interrogated about their alleged links with Iran's nuclear program.

Pakistan, a nuclear-armed nation, has been accused of sharing its technological know-how with other nations, a charge it fiercely denies. The KRL is the country's main nuclear weapons laboratory where uranium is enriched, according to the Federation of American Scientists (search).

Working with the International Atomic Energy Agency (search), the Iranian government recently agreed to sign an additional protocol of the Nuclear Nonproliferation Treaty, another step toward fulfilling its commitment to allowing unrestricted inspection of its nuclear facilities.

The United States suspects Iran of conducting a secret program to build nuclear bombs, and the IAEA has identified Russia, China and Pakistan as probable sources for equipment used by Iran for possible nuclear weapons development, according to diplomats.

Masood Khan, Pakistan's Foreign Ministry spokesman, said the two scientists were being "debriefed," not questioned as suspects. But he refused to discuss their cases.

On Thursday, three officials reached in separate telephone calls at the Khan Research Laboratories in Kahuta, a town 20 miles southeast of Islamabad, declined to discuss the reported detention of the two nuclear scientists.

In its report, The Dawn newspaper in Karachi said that Farooq and Chohan have been missing from the Khan Research Laboratories for a week.

The Nation said the security forces who took Farooq into custody at his home included foreigners. The Dawn said they may have been FBI agents.