A Pakistani nuclear scientist suspected of links to Islamic extremists met Usama bin Laden twice in Afghanistan but did not reveal any nuclear secrets, the scientist's son asserted Monday.

Sultan Bashiruddin Mehmood, who retired from Pakistan's Atomic Energy Commission in 1999, did not tell his family that he had met with bin Laden in 2000 and 2001, his son, Dr. Asim Mehmood, told The Associated Press.

He said the family learned about the meetings after Pakistani authorities detained his father in October to investigate possible ties to bin Laden's Al Qaeda network and its efforts to obtain nuclear technology.

The younger Mehmood said that to his knowledge, his father never discussed nuclear technology with bin Laden, and he insisted his father never revealed any nuclear secrets.

"These are all allegations. There is no truth in them," he said.

U.S. officials have long been suspicious of the elder Mehmood's contacts with bin Laden, according to Pakistani officials who spoke on condition of anonymity.

The U.N. Security Council ordered the assets of Ummah Tameer-e-Nau, a charity Mehmood organized after his retirement, frozen in December after the United States declared it an organization with terrorist ties.

When he retired, Mehmood was the director of the Khoshab nuclear reactor, a heavy water and natural uranium research reactor in Punjab province. The plant is believed to be involved in the production of plutonium and tritium for advanced compact nuclear warheads.

Last fall, Mehmood was repeatedly taken into custody, questioned and released only to be detained again. When he was last released, in mid-December, he was told he could not leave the Islamabad area or meet with politicians and journalists, his son said.

According to his son, Mehmood went to Afghanistan in 2000 in connection with Ummah Tameer-e-Nau, or Nation Builders, which planned ventures including a flour mill and irrigation projects. He said Mehmood sank his savings in the ventures and hoped to make a lot of money.

In 2000, Mehmood met bin Laden by chance at a mosque in Kandahar and was invited to dinner, his son said. He said his father traveled to Afghanistan four or five times and met bin Laden a second time the following year.

The son said his father also met Taliban supreme leader Mullah Mohammed Omar, and that he wanted to interest bin Laden in financing a polytechnic college in the Afghan capital, Kabul. "But Usama was not interested," he said.

"Usama might have tried to get his support in the nuclear field. But despite being religious minded, my father wasn't trapped," he said. However, he said he had no reason to believe bin Laden did seek any information about nuclear technology from his father.

Pakistani authorities say Mehmood did not have the specialized knowledge necessary to build a nuclear weapon. In January, the government decided not to prosecute him but to keep him under tight surveillance.

"We tried to convince him that hazardous travels are not good in old age," Asim Mehmood said. "We never realized that they will bring so much trouble. I think he should not have been that reckless."