First peace mediation efforts were started by the Russian President , Boris Yeltsin and Kazakhstan President , Nursultan Nazarbayev in September 1991 . After peace talks in Baku , Ganja , Stepanakert ( Khankendi ) and Yerevan on 20 – 23 September , the sides agreed to sign the Zheleznovodsk Communiqué in the Russian city of Zheleznovodsk taking the principles of territorial integrity , non-interference in internal affairs of sovereign states , observance of civil rights as a base of the agreement . The agreement was signed by Yeltsin , Nazarbayev , Mutalibov , and Ter-Petrosian . The peace efforts came to a halt due to continuing bombardment and atrocities by Azerbaijani OMON in Stepanakert and Chapar in late September . With the final blow being the Azerbaijani MI-8 helicopter shoot down near the village of Karakend in the Martuni District with a peace mediating team consisting of Russian , Kazakh observers and Azerbaijani high-ranking officials on board
Azerbaijani MI-8 helicopter shoot down
1991 Azerbaijani Mil Mi-8 shootdown
Nagorno-Karabakh War