Pakistan's top scientist Abdul Qadeer Khan, involved in clandestine nuclear sales, has reportedly suffered a heart attack.

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"Dr Khan is under treatment at his residence and his condition is stated to be critical," a local daily quoted officials of an hospital attached to Khan Research Laboratories, formerly headed by Khan, as saying.

The officials said in view of his "poor cardiac" condition, a heart specialist along with a cardiac machine was sent to the nuclear scientist's residence.

Khan has been suffering from pain in his left hand ever since he was questioned by intelligence agencies for his alleged involvement in transferring nuclear technology to other countries, The Dawn said.

Khan met President Pervez Musharraf a fortnight ago and admitted his guilt. He confessed his involvement in nuclear proliferation in an address to the nation on the state television.

The military ruler has since pardoned him.

The newspaper said Khan had never suffered from any cardiac problem all these years, but he often felt pain in his left hand.

"Dr Khan was holding his left hand when he was shown the last time on television after his meeting with President General Pervez Musharraf," it said.