BEIRUT - Syrian government forces killed at least 95 civilians, many in cold blood, and destroyed hundreds of houses in a two-week offensive in the northern province of Idlib during ceasefire negotiations, Human Rights Watch said on Wednesday.The New York-based advocacy group said war crimes were committed during the offensive against opposition strongholds in March and April as international peace envoy Kofi Annan was trying to end Syria's year-long conflict.In each attack, government forces used numerous tanks and helicopters and would stay in towns for one to three days before proceeding to the next town, the statement said.Graffiti left by soldiers in all the affected towns indicate the operation was led by the 76th Armored Brigade, it added."The circumstances of these cases indicate that government forces failed to distinguish between civilians and combatants and to take necessary precautionary measures to protect civilians. Government forces did not provide any warning to the civilian population about the attacks," the statement said.The Syrian government has not commented on the Human Rights Watch report. It accuses foreign-backed armed groups of being behind the violence and of killing more than 2,600 soldiers and police since the revolt against Syrian President Bashar Assad began. The United Nations says Assad's forces have killed more than 9,000 people since the uprising started in March, 2011."In nine separate incidents documented by HRW, government forces executed 35 civilians in their custody. The majority of executions took place during the attack on Taftanaz, a town of about 15,000 inhabitants northeast of Idlib city on April 3 and 4," the group said in a report.HRW researchers observed bullet marks on the wall that formed a row 50 to 60 cm (20 to 24 inches) above the floor, it added, roughly the height of a kneeling person. "While diplomats argued over details of Annan's peace plan, Syrian tanks and helicopters attacked one town in Idlib after another," Anna Neistat, associate director for program and emergencies at HRW, said in a statement accompanying the report based on an Idlib field investigation conducted in late April."Everywhere we went, we saw burnt and destroyed houses, shops and cars, and heard from people whose relatives were killed. It was as if the Syrian government forces used every minute before the ceasefire to cause harm," she said.