(CNN) -- A purported 1998 letter from a North Korean military official suggests that North Korea obtained nuclear technology not just through a renegade Pakistani nuclear expert, but also by paying bribes to top Pakistani generals.
Analyst Simon Henderson, with the Washington Institute for Near East Policy, said he was forwarded the letter four years ago by A. Q. Khan -- often called the father of Pakistan's nuclear weapons program.
"I was astounded," said Henderson, who has corresponded with Khan but is only now sharing the letter with the media. "I thought to myself, this is either absolutely authentic, or a most amazing forgery."
CNN was unable to confirm the authenticity of the document.
The letter, written in English with no letterhead, purports to be from the head of North Korea's military acquisitions, and is addressed to Khan. It informs him that bribes have been given to two Pakistani military officials, and calls on him to forward nuclear components to North Korea.
"The 3 millions dollars have already been paid" to one top general, the purported letter says, and another general has been given "half a million dollars and three diamond and ruby sets."
Now, the letter continues, it is time for Khan to deliver to the North Koreans.
"Please give the agreed documents, components etc. to (a North Korean official) to be flown back when our plane returns after delivery of missile components."
If true, the letter suggests that Pakistan's spreading of nuclear know-how to North Korea in the 1990s was not just the work of one renegade nuclear physicist, but had the blessing of top military officials in the country as well.
But is the letter genuine?
Both of the Pakistani generals named in the letter denied the allegations -- both in statements to the Washington Post, which first reported on the letter, and to Reuters, calling the claim "wrong" and "totally false."
And a spokesman for Pakistan's foreign ministry told reporters Thursday, "My only comment is that it is totally baseless and preposterous."
But a U.S. official contacted by CNN says the letter "appears to be authentic," and that the U.S. long suspected Pakistan's military was complicit in A. Q. Khan's alleged passing of nuclear secrets.
Bruce Riedel, who was the National Security Council's senior director for Near East and South Asian Affairs at the time, called the letter unproven, but plausible.
"The notion that A. Q. Khan was doing all of this himself has always been ludicrous," said Riedel, who is now at the Saban Center at the Brookings Institution.
Riedel went on to warn that the proliferation risk from Pakistan continues.
"The Pakistani military is riddled with jihadist sympathizers, and with penetrations by jihadist groups like al Qaeda," he said. "And the ultimate prize, for any terrorist in Pakistan, is a nuclear weapon."
Last month, Joint Chiefs of Staff Chairman Adm. Mike Mullen told reporters that one of the things he fears in the future is the proliferation of Pakistan's nuclear technology, and "the potential that it could fall into the hands of terrorists -- many of whom are alive and well and seek that in that region."
Pakistani officials have described their nuclear weapons installations as safe.
Seven years ago, Khan admitted to selling nuclear technology in a nationally televised speech, and said he alone was responsible.
"Khan was willing to sell the wherewithal to make nuclear weapons to very dangerous regimes," said former International Atomic Energy Agency inspector David Albright. "And he succeeded in transferring dangerous technology to North Korea, Libya, and Iran."
Khan was pardoned, although he was placed under house arrest. But in recent years, he has distanced himself from his confession.
In an interview with CNN in 2008, he said he had merely introduced foreign governments to suitable suppliers, and he painted himself as the fall guy for Pakistan.
"I was advised by some good friends that if I take the blame, things would die down," he said.
And last week, he flatly told Der Spiegel by email: "I did not indulge in proliferation."
"He's constantly trying to shift the blame to others," said Albright, who now heads the Institute for Science and International Security.
Albright says that while the purported bribe letter looks real, and matches what he knows of the chronology of nuclear deals between North Korea and Pakistan, "he certainly could have forged it. I mean, he's the origin of this letter, and all we have is his word."
"You have to kind of evaluate this letter very carefully, and not accept it at face value," he said. "Because Khan has a lot of incentive to blame others."
CNN's Pam Benson contributed to this report