A US Air Force OC-135 observation aircraft conducted an "extraordinary flight" Thursday under the Open Skies treaty "to reaffirm US commitment to Ukraine" amid Russia-Ukraine tensions, the Pentagon said.
Although the Open Skies Treaty gives each of the 34 state parties the right to gather information about the military forces and activities of other state parties, an extraordinary flight allows for countries to conduct the flights on a bilateral basis, in this case with the agreement of just Ukraine and the US.
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Russia, a signatory to the treaty, would have to approve a normal flight as part of a larger package that also includes the proposed flights of all 34 parties to the treaty.
"The timing of this flight is intended to reaffirm US commitment to Ukraine and other partner nations," Pentagon spokesman Eric Pahon told CNN.
"Russia's unprovoked attack on Ukrainian naval vessels in the Black Sea near the Kerch Strait is a dangerous escalation in a pattern of increasingly provocative and threatening activity," he added.
The last such "extraordinary" observation flight over Ukraine took place in 2014 as part of the US response to Russia's military intervention in Crimea, according to Pahon.
The Defense Department said US, Canadian, German, French, United Kingdom, Romanian and Ukrainian observers were aboard the aircraft during the observation flight. This flight was requested by the Arms Control Directorate of the Ukrainian General Staff.
A total of 25 US military personnel took part in the flight, including eight Defense Threat Reduction Agency personnel and a 17-person air crew from the 55th Wing out of Offutt Air Force Base, Nebraska, Pahon said.
The flight is just the latest US military effort aimed at pushing back at Russia amid heightened tensions in the region. Last month, Russia seized Ukrainian ships and detained Ukrainian sailors following a clash in the Kerch Strait, which connects the Black Sea to the Sea of Azov.
On Wednesday, the US Navy sailed the guided missile destroyer USS McCampbell near contested waters in the Sea of Japan, an action aimed at challenging Russian territorial claims
Additionally, CNN reported on Wednesday the US has begun making the necessary preparations to sail a warship into the Black Sea.
CLARIFICATION: This story has been updated to make clear Russia would have to approve a flight under the Open Skies treaty as part of a larger package of flights.