BELGRADE, Serbia

A Russian transport aircraft delivered another round of the Pantsir S1 air defense system to Serbia on Tuesday.

Serbia received the first of six shipments of the anti-aircraft defense system Saturday under an agreement signed with Russia in late 2019.

The second was delivered to the country by An-124 Ruslan aircraft, registered with the RA-82038, which already delivered the first part to the Batajna military airport.

The U.S. repeatedly warned Serbia that the purchase of Russian weapons "poses a risk" of U.S. sanctions.

The State Department called on allies and partners to forgo transactions with Russia that could lead to sanctions under the U.S. Opposition through Sanctions Act (CAATSA).

"In discussions with senior government officials, we have repeatedly expressed concern that Serbia is buying Russian military equipment, including the purchase of the Pantsir system," a State Department spokesman told the Voice of America agency.

The European Union previously said to progress on the road to European integration, "Serbia needs to align its foreign policy with the EU's foreign policy, in accordance with the negotiating framework."

Serbia emphasized the missile system is a guarantor of long-term peace in the region.

The missile system will be used to protect critical points such as airports and command and contact centers from possible attacks by manned and unmanned aircraft as well as helicopters, according to Serbia.

The Pantsir S1 was exhibited alongside Russian S-400 missile systems during a military exercise in Serbia in October.