The situation in Nagorno Karabakh region causes serious concern; the sides should avoid further escalation, Collective Security Treaty Organization (CSTO) Secretary General Nikolai Bordyuzha said Sunday, December 27, Sputnik International reports.

"We are greatly concerned about the situation in the Caucasus, especially in connection with the Karabakh conflict, with heavy weapons, tanks used and casualties registered on the contact line," Bordyuzha said in an interview with Rossiya-24 news channel.

He added that political resources of the CSTO states should be used to prevent further destabilization of the situation, as well as "to ensure that this conflict does not develop into large-scale military clashes."

The CSTO is an intergovernmental military alliance formed in 1992 with six members at present: Russia, Tajikistan, Kazakhstan, Kyrgyzstan, Armenia and Belarus, as well as two observer states – Afghanistan and Serbia.