I always just assumed they were Soviet fighters-- since they sported a red star --operating out of a friendly country's base in the Indian Ocean area (such as Yemen, island of Socotra, where the Soviets really had a military base, or-- as mechajutaro said --Iran, etc.).

Also, in real life, the enemy MiGs were actually American F-5 Tiger II fighters painted to look like enemy planes; and the designation "MiG-28" was completely made up, as NATO only designated MiG fighters using odd numbers (MiG-21, MiG-23, MiG-25, MiG-27, MiG-29, all of which were real fighters, some of which are still flown by former East Bloc nations today).

The more you know (cue cheesy Public Awareness music)