WASHINGTON The US government has accused Pakistan of illegally modifying US-made anti-ship missiles to make them capable of striking land targets and thus creating a new threat for India, The New York Times reported late 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.

At the center of the row were Harpoon anti-ship missiles that were sold to Pakistan by the administration of former US president Ronald Reagan as a defensive weapon during the Cold War in the 1980s, the report said.

US military and intelligence officials say they suspect that Pakistan has modified the missiles in a manner that would be a violation of the Arms Control Export Act, the paper said.

Pakistan has denied the charge, saying it developed the missile itself. But 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 missile would be a significant new entry into Pakistans arsenal against India, The Times said. It would enable Pakistans navy to strike targets on land, complementing the sizable land-based missile arsenal that Pakistan has developed.

That, in turn, would be likely to spur another round of an arms race between the nuclear-armed rivals that the United States has been trying to halt, the paper noted.

'The potential for proliferation and end-use violations are things we watch very closely,' The Times quotes an administration official as saying.

'When we have concerns, we act aggressively.'

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.