BELGRADE, Serbia (AP) — Serbia has thanked Russia for sending its sophisticated anti-aircraft missiles for joint air defense drills, the first-ever such deployment by Moscow.

Serbian President Aleksandar Vucic visited a military airport near Belgrade on Friday, saying he was impressed by what the Russian air defense systems can do.

Vucic said he was "thankful to our Russian friends for drastically boosting our defense capabilities."

The Russian Defense Ministry said that the long-range S-400 and the short-range Pantsyr-S systems are taking part in the Slavic Shield-2019 exercise that envisages joint action by the Russian and Serbian militaries to fend off air attacks. The S-400 is to be returned to Russia after the six-day drills.

Serbia is Russia's only remaining ally in the Balkans despite a proclaimed goal of joining the European Union.