Pakistan is United States' 'most serious national proliferation problem' with Islamabad's role being instrumental in the Iranian nuclear weapons programme, an expert on nuclear non-proliferation has told a US Congressional panel.

"If I had to answer who's our most serious national proliferation problem now, in terms of spreading technology, you'd have to say Pakistan -- not because necessarily the government's policy is to do so but they have allowed Pakistanis to do so," said Joseph Cirincione, the vice president for National Security at the Centre for American Progress.

"If it was not for Pakistan, we would not have an Iranian nuclear programme," Cirincione told lawmakers in the House Foreign Affairs Committee during a panel hearing on nuclear weapons non-proliferation.

The security expert also acknowledged the covert role of China in Pakistan's nuclear weapon programme.

"I completely agree that if it was not for China, Pakistan would not have a nuclear programme now. As far as we know, China is no longer aiding Pakistan in its nuclear weapons programme," the non-proliferation specialist told lawmakers.

"China is not a serious proliferation threat today. They used to be. When Mao Zedong was in charge, they were pro-proliferation. When China exploded theirs (bombs) they changed that position and became, sort of, neutral on proliferation," Cirincione said at the Congressional hearing.

"But they still aided their allies like Pakistan and were a serious problem. Now, they have firmly adopted non-proliferation policies. They have integrated into every aspect of the nonproliferation regime," he said.

Besides Cirincione, the other two members of the panel were former Senator Sam Nunn, Chairman and CEO of the Nuclear Threat Initiative and Henry Sokolski, Executive Director of the Non-Proliferation Policy Education Centre.       
Referring to Congresswoman Sheila Jackson-Lee question on changing the attitude of countries like Pakistan, Sokolski argued that it was beyond just money.

"If it was just money, I think we would have solved a lot of these problems. In particular, Pakistan acts frequently badly when it feels encircled, or it feels as though India is getting the upper hand on its sovereignty and its ability to exist," said the non-proliferation specialist.

"One of the reasons you should be concerned about the connection between India and Iran is that Pakistan sees it as a threat. It sees India's cooperation with Iran as encirclement," the expert said.

"The committee's firm words on India's need to cut off its formal military ties and possible energy investments in Iran caught many off guard. Nonetheless, they were right on target," Sokolski noted.

He argued that the Chairman of the House Panel and the Committee have a right to demand that India forswear its formal military and energy investment ties with Iran as the bare minimum for US strategic partnership.