North Korea bribed top Pakistani military officials to have access to sensitive nuclear technology and equipment in the late 1990s, claims disgraced nuclear scientist A.Q. Khan.
Washington Post reported that Khan has made available documents that show he personally transferred over $3 million in payments by North Korea to senior officers in the Pakistani military.
The newspaper said that Khan has also released a copy of a North Korean official's 1998 letter that give details of the clandestine deal.
While Western intelligence officials think the letter is authentic, Pakistani officials have called the letter a fake.
The media report said that if the letter is genuine, it would show corruption related to nuclear weapons.
The letter dated July 15, 1998 and marked 'Secret' said that the '3 millions dollars have already been paid' to one Pakistani military official.
"Half a million dollars" and some jewellery had been given to a second official, said the letter bearing the apparent signature of North Korean Workers' Party Secretary Jon Byong Ho.
The text reads: "Please give the agreed documents, components, etc. to .?.?. (a North Korean Embassy official in Pakistan) to be flown back when our plane returns after delivery of missile components."
Former Pakistani military chief Jehangir Karamat, who is named as the recipient of the $3 million payment, said the letter is untrue.
Karamat said that Khan has tried to shift blame on others and added that the letter's allegations were "malicious with no truth in them whatsoever".
Another top military official, retired Lt. Gen. Zulfiqar Khan, termed it "a fabrication".
Khan's written account said the exchange of North Korean cash for Pakistani technology came up during a squabble in 1996 over delays in Pakistan's payment to North Korea for some medium-range missiles.
In 2000, the US accused Pakistan of providing nuclear weapons' technology to North Korea in exchange for ballistic missile technology.
A year later, the Pakistani government announced it had dismissed Khan as the head of Khan Research Laboratories, a move that drew strong criticism from religious forces.
Khan, who mentored Pakistan's nuclear programme, had in January 2004 confessed to having sold the country's nuclear secrets to Libya, Iran and North Korea.
On Feb 5, 2004, President Pervez Musharraf announced he had pardoned Khan, who is widely seen as a national hero in Pakistan.