"In light of the dramatic escalation in violence along the Line of Contact in April, we express concern over continuing armed incidents, including reports on the use of heavy weapons, and strongly condemn the use of force or the threat of the use of force", said in the statement.
The Co-Chair countries are prepared to host a meeting of the Presidents of Armenia and Azerbaijan when they are ready.
"Continuous and direct dialogue between the Presidents, conducted under the auspices of the Co-Chairs, remains an essential element in building confidence and moving the peace process forward", said in the statement.
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 1994 ceasefire agreement was followed by peace negotiations.
Armenia has not yet implemented four UN Security Council resolutions on withdrawal of its armed forces from the Nagorno-Karabakh and the surrounding districts.