BELGRADE, Serbia (AP) — Serbia has received a sophisticated anti-aircraft system from Russia, despite possible U.S. sanctions against the Balkan state, which is formally seeking European Union membership.

Serbian President Aleksandar Vucic told the pro-government TV Prva on Sunday that the Pantsir S1 air-defense system was purchased after suggestions from Russian President Vladimir Putin.

“Buy Pantsir, it showed its best efficiency in Syria,” Vucic quoted Putin as saying during one of their recent, frequent meetings.

“This anti-aircraft system is very efficient for targeting drones which are becoming crucial in modern warfare,” Vucic said.

Despite seeking to join the EU, Serbia under Vucic’s populist leadership has strengthened close political and military ties with its Slavic ally Russia.

Serbia has pledged to stay out of NATO and refused to join Western sanctions against Russia for its policies in Ukraine.

Russia’s arming of Serbia is watched with unease in the West amid growing tensions in the Balkans which went through a devastating civil war in the 1990s. NATO intervened in Serbia to stop a bloody Serb crackdown against Kosovo Albanian separatists in 1999.

U.S. officials have openly spoken about introducing sanctions against Serbia in case Moscow sells more arms to the country, especially with weapons that could jeopardize the security of neighboring NATO-member states.

Vucic said he hoped there would be no sanctions because he has spoken openly about the Pantsir purchase. He said he believed the sanctions threat was focused on possible purchase of the S-400 anti-aircraft systems that have a much larger range and are more offensive weapons.

The delivery on Saturday of two of the purchased six Russian missile systems comes just days after Russia’s defense minister, Sergei Shoigu, visited Belgrade where he declared that the military cooperation between the two states has reached a “fundamentally” new level.

Pantsir is a rapid-fire missile system intended for defense against cruise missiles, drones and low flying aircraft with a range of about 20 kilometers (12 miles).