Iranian observers claim planes shown in videos and images from the incident show the two harassing planes were (American) F-15s. The incident happened just as the planed entered Syria.
Video shows moments unidentified planes harass Iranian passenger plane headed to Lebanon.
The Interception seems to have happened over US Army Base in Southern Syria aka in Al-Tanf
The Drop in altitude was at 16:29 (Interception time) after it passed Al Tanf at 16:12 (Local time) Iranian Military Press says that Mahan Airlines confirmed that the Fighter Jets introduced themselves as Americans.