Organization of Islamic Cooperation (OIC) urged Armenia to immediately liberate occupied territories of Azerbaijan, Iyad bin Amin Madani, secretary general of the OIC said, Turkish news agency Anadolu reported.
"I am very concerned about the exacerbation of the Nagorno-Karabakh conflict", he added.
The conflict between the two South Caucasus countries began in 1988 when Armenia made territorial claims against Azerbaijan. As a result of the ensuing war, in 1992 Armenian armed forces occupied 20 percent of Azerbaijan, including the Nagorno-Karabakh region and seven surrounding districts.
The two countries signed a ceasefire agreement in 1994. The co-chairs of the OSCE Minsk Group, Russia, France and the US are currently holding peace negotiations.
Armenia has not yet implemented the UN Security Council's four resolutions on withdrawal of its armed forces from the Nagorno-Karabakh and the surrounding districts.