The architect of Pakistan's nuclear weapons program claims North Korea paid bribes to senior Pakistani military officials in return for nuclear secrets in the 1990s, the Washington Post said Wednesday.

The Post said documents released by nuclear scientist Abdul Qadeer Khan purportedly show him helping to transfer more than $3 million to senior officers, who he says then approved the leak of nuclear know-how to Pyongyang.

Khan passed a copy of a North Korean official's letter to him in 1998, which details the transaction, to former British journalist Simon Henderson, who then shared the information with the Washington Post, the newspaper said.

The Post cited Western intelligence officials as saying they believed the letter was accurate, but said Pakistani officials have denied Khan's claims, arguing that it is a forgery.

Pakistani foreign office spokeswoman Tehmina Janjua on Thursday called the allegations "baseless" and said they frequently reappear in the media.

"This is totally baseless and preposterous," she said during a weekly press briefing.

Khan -- considered a national hero in Pakistan because he played a key role in the creation of the Islamic world's first atomic bomb -- has long been at odds with Pakistani officials who have insisted he acted alone.

Khan admitted on national television in 2004 that he passed atomic secrets to North Korea, Iran and Libya, but later retracted his remarks and in 2009 was freed from house arrest, although he was asked to keep a low profile.

Those secrets are nevertheless widely believed to have allowed North Korea to develop a uranium route alongside its existing plutonium weapons program.

The letter, dated July 15, 1998, marked "Secret," and purportedly signed by North Korean Workers' Party Secretary Jon Byong Ho, says "the 3 millions (sic) dollars have already been paid" to one Pakistani military official and "half a million dollars" and some jewelry had been given to a second official.

It then says: "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."

In written statements to Henderson, Khan describes delivering the cash in a canvas bag and cartons, including one in which it was hidden under fruit.

Jehangir Karamat, a former military chief said to have received the $3 million payment, and Lieutenant General Zulfiqar Khan, the named recipient of the other payment, both denied the letter's authenticity to the Post.

The Post report could further heighten tensions between Pakistan and the United States, which has long been concerned about Islamabad's nuclear arsenal.

The two uneasy allies have been increasingly divided since the US commando raid in May that killed Al-Qaeda chief Osama bin Laden in a compound near Islamabad where he had been living for years.