Fighting in Syria escalated on Wednesday, with troops loyal to President Bashar al-Assad suffering their worst loss of life since the start of the failed United Nations-mandated cease-fire three weeks ago.

Rebel forces reportedly killed 20 troops in a series of pre-dawn raids, including two colonels and 15 soldiers during an attack in the northern city of Aleppo, according to the Syrian Observatory for Human rights.

The latest clashes come as activist group Human Rights Watch (HRW) accused the Syrian army of committing war crimes in a new report documenting the killing of at least 95 civilians in Idlib province two weeks before the start of the April ceasefire.

In its 38 page report, They Burned My Heart: War Crimes in Northern Idlib during Peace Plan Negotiations, HRW claim government troops carried out, dozens of extrajudicial executions, killings of civilians, and destruction of civilian property that qualify as war crimes, as well as arbitrary detention and torture.

While diplomats argued over details of Annan's peace plan, Syrian tanks and helicopters attacked one town in Idlib after another, said Anna Neistat, associate director for program and emergencies at HRW.

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.

The report comes a day after chief United Nations peacekeeper Herve Ladsous condemned both the Syrian government and rebel forces for their continued violation of the cease-fire agreement and Kofi Annan's negotiated six-point peace plan.

Ladsous told reporters that both sides of the conflict were responsible for creating an atmosphere of appalling violence -- but he added that despite the bloodshed, the small UN presence was having a dampening effect.

Ladsous noted that the UN would also accelerate the deployment of peacekeepers to the war-torn country, with all 300 on the ground by the end of May.

The UN estimates over 9,000 people have been killed during the 13-month rebellion, with opposition groups estimating the number may be as high as 11,000.