Washington is taking a close look at reports that Pakistan used US-supplied F-16 fighter jets in the recent confrontation with India, according to State Department Deputy Spokesperson Robert Palladino.
"We've seen those reports and we're following that issue very closely" Palladino told reporters at a Department briefing on Tuesday in Washington. "We're taking a look and we're going to continue to take a look".
However, he added that he could not confirm anything because "as a matter of policy, we don't publicly comment on the contents of bilateral agreements that we have in this regard involving US defence technologies nor the communications that we have with other countries about that".
"We reiterate our call for Pakistan to abide by its UN Security Council commitments to deny terrorists sanctuary and to block their access to funds", Palladino said.
He said that a "lot of" private diplomacy was taking place between US and India and Pakistan in addition to ongoing high-level contacts through the embassies in Washington and in New Delhi and Islamabad to ease the tensions.
On Thursday, Air Vice Marshal R.G.K. Kapoor said in New Delhi that Pakistan sent F-16s, JF-17 Thunders and Mirages last Wednesday to the Line of Control (LoC) in Kashmir and an F-16 was shot down by the Indian Air Force (IAF).
The IAF showed a piece of an AMRAAM missile which landed in an Indian military compound when Pakistan launched an attack along the LoC. Of the jets in Pakistan's arsenal, the AMRAAM can be used only with F-16. The IAF also said it identified F-16s operating there through their electronic signatures.
An IAF MiG-21 was lost in the encounter and the parachute of the pilot, Wing Commander Abhinandan Varthaman drifted into Pakistani-held territory, Kapoor added.
Varthaman was captured by Pakistan, but returned to India on Friday under intense international pressure.
A Pakistani spokesperson denied last week that it had used F-16 in the sorties against India, but did not identify the planes used.
On Monday, Pakistan's Ambassador Asad Majeed Khan said at a Washington think tank, "I am not aware of request from the US side about the F-16s.
At his briefing, Palladino said that the US continues "to urge both sides to continue to take steps to de-escalate the situation, and that includes through direct communication".
He said that in Hanoi last week Secretary of State Mike Pompeo "led diplomatic engagement directly, and that played an essential role in de-escalating the tensions between the two sides".
"He spoke with leaders in both countries, and that included the Indian Minister of External Affairs (Sushma) Swaraj, National Security Advisor (Ajit) Doval, and Pakistani Foreign Minister (Shah Mehmood) Qureshi", Palladino added.
After Pompeo's round of talks with Indian and Pakistani leaders on Wednesday night, Pakistani Prime Minister Imran Khan announced on Thursday that he was returning Varthaman to India.
Short for Advanced Medium-Range Air-to-Air Missile, AMRAAM missiles were obtained by Pakistan from the US in 2010.
Its manufacturer Raytheon says that it has an "advanced active guidance" system and its design "allows it to quickly find targets in the most combat challenging environments".
Pakistan has bought several batches of F-16 planes since 1982, and 85 of the jet made by Lockheed Martin Corp are estimated to be in the Pakistan Air Force (PAF) fleet.
In 2016, US Congress ended subsidies for F-16 sales to Pakistan.
US-Pakistan military ties are faltering because of Islamabad's continued support for terrorists. President Donald Trump cut $300 million in military aid to Pakistan in September 2018, saying it was not doing enough to rein in terrorists attacking Afghanistan, as well as US troops there.
Earlier, Congress had removed $500 million in funds given to Pakistan for supporting the operations of the US and its allies in Afghanistan.