They where not sent to Serbia, but at that time Yugoslavia at the overhaul facility in Zagreb(now Croatia). Yugoslavia was socialist, but US allied country and never part of "eastern Block" and Warsaw Pact. During that time, USA supported Iraq in war against Iran. Yugoslavia was perfect political choice to fix plains. USA also hired Yugo construction companies to build airports and military installations, even Including the Saddam's bunker. They where never delivered back because of the Gulf war 1 and sanctions. Iraq had Russian, but as well a lot of USA, French and British equipment. It was absurd than Iran had USA Phantom jets!