NATO said it "respects" Serbia's decision to hold joint air military exercises with Russia in which the Russian S-400 and Pantsir-S air-defense missile systems are being deployed.
Russia said the long-range S-400 and the short-range Pantsir-S systems are being used in the Slavic Shield-2019 exercise to test joint action by the Russian and Serbian militaries to fend off air attacks.
Russia’s Defense Ministry said the surface-to-air missile systems are stationed at the Batajnica base, outside the Serbian capital, Belgrade.
It is the first time that an S-400 battalion and a Pantsir-S battery have appeared in military drills outside Russia, the ministry said.
In a statement to RFE/RL, NATO's press office said the alliance and Serbia "are partners and we respect Serbia’s right to make sovereign decisions about exercises on its territory.”
“This is a matter for Serbia and Russia," the NATO statement said, adding that "Serbia is a NATO partner" and that the Balkan country has a “good and productive relationship” with the Western alliance.
The S-400 is to be returned to Russia after the six-day drills end on October 29.
Serbian President Aleksandar Vucic has said the Pantsir system was purchased by his government.
Serbia maintains strong political and economic relations with Russia despite a proclaimed goal of joining the EU. Belgrade has pledged to stay out of NATO and refused to join Western sanctions against Russia over Ukraine.