North Korea purchased millions of dollars of nuclear weapons technology from senior Pakistani military officials, says A.Q. Khan, the founder of Pakistan’s nuclear program. Khan has released documents and a copy of 1998 a letter written to him by a North Korean official, Jo Byong Ho, to back up his claim that two Pakistani military officials were paid $3.5 million as part of the secret deal. Khan gave the documents to Simon Henderson, an expert on Pakistan’s nuclear weapons program at the Washington Institute for Near East Policy, because he claimed his government has accused him of running a covert nuclear smuggling operation while denying any involvement. “He gave it to me because he regarded it as showing that the story, the perception that he had been a rogue operator was false,” said Henderson. The Washington Post, which obtained the documents and first reported on them Wednesday, said Khan’s assertions could not be independently verified, and the two Pakistani military implicated have dismissed the allegations as fabrications. Nevertheless, the revelation is bound to add to the strain on U.S.-Pakistan relations in the war against Islamic extremists in Afghanistan and Pakistan.