Pakistan on Sunday rejected US government claims that it illegally modified American-made missiles and said the accusations were part of a campaign to "malign it and its armed forces".
Modifications to anti-ship missiles made them capable of hitting land-based targets and thus threatening India, The New York Times said on Saturday.
Citing unnamed senior administration and congressional officials, the newspaper said the accusation was made in an unpublicized diplomatic protest delivered in late June to Pakistani Prime Minister Yousuf Raza Gilani.
"It appears to be a campaign by design to malign Pakistan and the armed forces to achieve some purpose," a senior Pakistani security official told AFP, asking not be named.
He said the Harpoon missiles were meant for maritime use and "there is no credible information to suggest that the navy might have changed the original purpose of the missile."
The New York Times said the missiles were sold to Pakistan by the administration of former US president Ronald Reagan as a defensive weapon during the Cold War in the 1980s.
US military and intelligence officials said they suspect that Pakistan has modified the missiles in a manner that would be a violation of the Arms Control Export Act in the United States, the paper said.
According to the report, US intelligence agencies detected on April 23 a suspicious missile test that appeared to indicate that Pakistan had a new offensive weapon.
The United States has also accused Pakistan of modifying US-made P-3C aircraft for land-attack missions, another violation of US law that the administration of President Barack Obama has protested, the report said.