The head of the U.N. observer mission in Syria said Monday he was \"extremely concerned\" about the continuing violence in Syria, particularly in Aleppo, the country\'s biggest city. \"I am extremely concerned about the continued violence in Syria, in particular the significant deterioration in Aleppo and its impact on the civilian population,\" Lieutenant General Babacar Gaye, interim head of the U.N. Supervision Mission in Syria, said in a statement. \"I urge the parties to protect civilians and respect their obligations under international humanitarian law,\" he said. \"Civilians must not be subjected to shelling and use of heavy weapons.\"