The United States Air Force flew an E-8C Joint Surveillance Target Attack Radar System (JSTARS) aircraft over eastern Ukraine in a reconnaissance mission on December 27, 2021.

Spokesman for US European Command Lt. Cmdr. Russ Wolfkiel told CNN that this was the first time the E-8C JSTARS has flown over Ukraine.

The surveillance flight happened two days after Russia announced it would withdraw 10,000 troops from its border with Ukraine.

An online aircraft tracker showed that the mission involved an E-8C battlefield surveillance plane and an RC-135V Rivet Joint signals intelligence aircraft.

While the Pentagon has not revealed exactly what intelligence the aircraft was gathering, Wolfkiel told CNN that the US "routinely operates aircraft in the Black Sea region in support of various US and coalition intelligence objectives."

Wolfkiel disclosed that the aircraft flew with the permission of the Ukrainian government, and that the flight stayed clear from the Donbas region where pro-Russian separatist forces from Ukraine operate.

This came as tensions rise over reports of Russia’s military build-up in its border with Ukraine, despite Russia claiming that it is withdrawing 10,000 troops from the border.

At the request of the Russian government, US president Joseph Biden is expected to speak on the phone with Russian president Vladimir Putin on the afternoon of December 30, 2021. The two presidents previously spoke via video call on December 7, 2021, where President Biden warned President Putin that if Russia decides to invade Ukraine, the US and European allies would impose “strong economic and other sanctions.”

On December 27, 2021, President Biden signed into law the annual military funding bill that includes $300 million in military aid to the Ukrainian Security Assistance Initiative, which provides training, equipment and support to Ukraine’s efforts to secure its borders.