Pakistan rejected charges that it had developed new illicit channels to upgrade its nuclear weapons programme and said it was interested in joining an influential anti-proliferation group.
Diplomats and nuclear experts said this week that Pakistan was using illicit channels to upgrade its nuclear weapons capability, despite efforts by the UN nuclear watchdog to shut down all illegal procurement avenues.
"This story is inaccurate and baseless," said Pakistani foreign ministry spokesman Jalil Abbas Jilani.
"Pakistan's nuclear programme is purely indigenous and does not rely on foreign sources." Mr Jilani said a team from the Nuclear Suppliers Group, a body that aims to control nuclear exports, had asked to visit Pakistan and this had been accepted.
Despite Islamabad's denials, analysts say that since Pakistan is outside the 1968 global nuclear Non-Proliferation Treaty (NPT), Islamabad has no choice but to buy nuclear components on the black market.
Pakistan first successfully tested a nuclear weapon in 1998 and remains under a strict embargo by the NSG, whose members include the world's major producers of nuclear-related equipment, such as the United States, Russia and China.
Global concerns about Islamabad's nuclear programme were triggered when it was revealed that Abdul Qadeer Khan, the father of Pakistan's atomic bomb, used a clandestine procurement network to supply Iran, Libya and North Korea with nuclear technology.
Last week Pakistan admitted that the now-disgraced Khan had supplied Iran with centrifuges used to produce enriched uranium for nuclear power plants or arms. But it subsequently rejected reports quoting diplomats in Vienna that Islamabad would hand over used centrifuge components to the UN International Atomic Energy Agency to help determine whether Iran's atomic programme is aimed at producing weapons, as Washington suspects, or is entirely peaceful as Tehran says.
The fresh controversy comes as US Secretary of State Condoleezza Rice was due in Islamabad later today to discuss Pakistan's key role in the US-led war on terrorism with President Pervez Musharraf.
Ms Rice's trip comes as the U.S. government is considering selling F-16s fighter jets to both India and Pakistan, a move that would be a final step toward tacit acceptance of both countries' possession of nuclear weapons. Washington blocked a sale of a batch of F-16s to Pakistan in the 1990s as a sanction against Islamabad's nuclear programme.