The newspaper on Monday published a report containing allegations that the so-called father of Pakistan's nuclear program, metallurgist Abdul Qadeer Khan, had played a key role in developing Iran's program.
Citing a French government report as well as active and former officials from Iran, Pakistan, the Middle East and the US, it also alleged that Pakistani generals had offered to share nuclear technology with Iran in 1989.
Pakistan's foreign ministry slammed the allegations as "false, irresponsible and obviously motivated."
It denied the report's claims that Khan had travelled to Iran to help develop gas centrifuges used to enrich uranium to transform it to weapons-grade material.
"A.Q. Khan... never set foot in Iran or ever met with any Iranian nuclear experts," the Pakistan foreign ministry said in a statement issued in Washington and Islamabad.
Claims by Iranian defector and former official Ali Akbar Omid Mehr that Khan had been given a villa on the Caspian Sea in reward for helping Iran were "baseless and fabricated... wild flights of fancy," the Pakistani statement said.
"Pakistan's commitment that it would not export any sensitive technologies to third countries remains unquestionable," it added.
Iranian, US and other foreign intelligence officials told the LA Times that Khan "travels frequently to Iran to share his expertise."
"Most recently... he has worked as a troubleshooter to iron out problems with the centrifuges and with weapons design," the paper said.
Two unnamed former senior Pakistani officials told the paper that Pakistani military commanders offered to sell nuclear weapons technology to Iran in 1989.
A French government report this year on Iran's nuclear program said there were "convincing indications about the origin of the technology - it is of Pakistani type."
A Middle Eastern intelligence official described Pakistan's role in Iran's nuclear program as "bigger from the beginning than we thought."
Khan, a maverick metallurgist who stole the blueprints of gas centrifuges from the Netherlands in the 1970s, was fingered by the US Central Intelligence Agency last year as a key contributor to North Korea's nuclear program.
A key Pakistani nuclear weapons facility named after Khan had sanctions announced against it by the US in March for allegedly helping North Korea develop its nuclear program.