The International Atomic Energy Agency, which monitors nuclear technology for the United Nations, is believed to have sought face-to-face interviews with Dr Khan but Pakistan has made it abundantly clear that it cannot allow such access to foreign nationals.

President Pervez Musharraf, who visited Washington last week, also reiterated Pakistan's position on this issue. In interviews to various US news outlets, he said that Islamabad can never allow any foreign government or international agency direct access to Dr Khan.

Last month, some US newspapers had reported that Pakistan might allow IAEA inspectors to inspect some of its nuclear facilities to determine if the network allegedly headed by Dr Khan had supplied equipment contaminated with enriched uranium to Iran.

Pakistan, however, rejected this report as totally baseless, saying that it cannot open its facilities to outsiders even for limited inspection. Then the Tehran Times reported that Pakistan might take some of its equipment to a third country, possibly Italy, for inspection.

This would help the IAEA determine if the equipment Iran purchased from the so-called Khan network were already contaminated or Iran was quietly enriching uranium at its facilities. Pakistan also rejected that report as incorrect. But now US newspapers are reporting that the IAEA has made an arrangement with Pakistan for sending written questions to Dr Khan and the answers he writes would be sent to the agency without tampering.

The IAEA believes that although this method may not be as useful as a direct access, it could help the agency untangle the network of manufacturers and middleman that supplied sensitive machinery and know-how to Libya, Iran, North Korea and perhaps others.

The report said that the IAEA was also making progress towards gaining access to a key member of the Khan network, Bukhari Sayed Abu Tahir, the Dubai-based businessman who is in custody in Kuala Lumpur.

Mr Abu Tahir has been held under a security act that prevents all contact with him. But investigators are now expecting to be allowed to see him. Meanwhile, Mohamed ElBaradei, director-general of the IAEA, has said his agency had agreed 'modalities' with Pakistan that should enable it to receive information from Dr Khan, but he refused to elaborate.

He said his agency was in talks with the Malaysian government as well on access to Mr Abu Tahir. He said the IAEA has to work through governments for information about the Khan network and so far both the Pakistani and Malaysian governments have been "quite cooperative."

The IAEA believes that Dr Khan and Mr Abu Tahir might provide information on customers of the illegal network that have not declared their nuclear programmes. "It's important for us to know who else got equipment and whether there are undeclared programmes," Mr ElBaradei said.

Libya, which abandoned its nuclear weapons ambitions a year ago, obtained designs for a nuclear weapon from the Khan-Tahir network. The Chinese originated blueprints are now in the US. The IAEA wants to know whether Iran and North Korea might have made a similar purchase.