In this Wednesday, April 6, 2016 photo, ground crew stands on the tarmac by a Mig 21 fighter jet, at the military airport Batajnica, near Belgrade, Serbia. Serbia's defense minister Zoran Djordjevic says Russian President Vladimir Putin promised to sign off on a delivery of fighter jets, battle tanks and armored vehicles to Serbia, which could trigger an arms race in the war-torn Balkans. ??z??zDefense Minister Zoran Djordjevic said Tuesday, March 28, 2017 that six MiG-29 fighter jets, 30 T-72 tanks and 30 BRDM-2 armored vehicles will be delivered soon. (AP Photo/Darko Vojinovic)