The United States wrote to Pakistan in August to express displeasure about its misuse of F-16 fighter aircraft, months after jets of that make were allegedly used in an aerial skirmish involving the Indian Air Force, U.S. News reported on Wednesday.

Aircraft of the Pakistan Air Force had violated Indian airspace in Jammu and Kashmir on February 27, a day after the Indian Air Force struck a camp of the Jaish-e-Mohammad terrorist group across the border. Pakistan had then rejected India’s claims that it had used US-supplied F-16 fighter jets in the dogfight. The use of the F-16 jets would violate the terms governing their sale by the US.

The United States said in March that it was closely following reports that Pakistan used F-16 fighter jets. Pakistan, however, claimed it had used the JF-17 Thunder combat aircraft, which were developed jointly by the Pakistan Aeronautical Complex and China’s Chengdu Aircraft Corporation.

According to documents accessed by U.S. News, Department of State official Andrea Thompson wrote to Pakistan’s Air Chief Marshal Mujahid Anwar Khan in August, accusing Islamabad of using the F-16s and jeopardising the two countries’ shared security. Thompson was then the under-secretary of State for Arms Control and International Security Affairs. She is no longer in the government.

Though the letter did not specifically mention the February dogfight, an unidentified person who saw the letter told U.S. News that it served as a direct response to the United States’ concerns about the use of F-16 jets over Kashmir.

In the letter, Thompson said that Pakistan had moved the F-16s and other US-made missiles to unapproved forward operating bases in defiance of its agreement. She warned Pakistan that such behaviour could put the weapons into the hands of malign actors.

Neither the State Department nor the Pakistani Embassy in the United States responded to requests for comment by U.S. News.

Diplomatic officials said it was not surprising that the letter did not explicitly mention the Kashmir incident, because acknowledging it formally would have triggered formal procedures to reprimand Pakistan.

Pakistan had claimed it had chosen “non-military targets” and only meant to show its capability. However, India had said that Pakistan had targeted military installations.

On February 27, the Pakistani military claimed it had shot down two Indian Air Force jets – one had crashed in Pakistan-occupied Kashmir and the other fell in Jammu and Kashmir. India maintained that Pakistan shot down only one MiG-21 aircraft while the Indian Air Force shot down a Pakistani F-16 jet during the dogfight.

During the same skirmish, Pakistan had captured Indian Air Force pilot Wing Commander Abhinandan Varthaman, who was released and returned home on March 1.