This was disclosed on Tuesday by US Assistant Secretary of State for Public Affairs P J Crowley, who said that the Obama administration has taken up the matter with Pakistan.
His comments came two days after the New York Times reported that Pakistan had illegally modified the harpoon anti-ship missile to expand its capacity to strike land targets for potential use against India.
"This is something that we take very seriously. We have raised the issue with the Pakistani government. The (Pakistan) government has responded with an agreement in principle for mutually agreed inspections," Crowley told PTI when asked about the report.
"In this particular case, we have some concerns. We shared them with the government of Pakistan. The government of Pakistan has been responsive," he said, adding, "We would wait and see if those inspections can address the concerns that we have raised."
The newspaper, quoting unnamed administration officials, had said the US also accused Pakistan of modifying American- made P-3C maritime surveillance aircraft for land-attack missions in a violation of the American laws, including the Arms Control Export Act.