The Syrian rebel group Jaish al Islam announced on Friday Assad forces were mobilising to take more opposition-held territory since a cessation of hostilities deal carried into action on last Saturday.
"There are big violations by the regime and occupation of new areas, the use of all types of weapons, particularly planes and barrel bombs in some areas, and mobilisations to occupy very important strategic areas," Mohamad Alloush, head of the group's political office, told Reuters.
He also added humanitarian aid delivered recently to opposition-held territory besieged by the government "is not enough to meet 10 percent of the needs, and nothing has entered most of the areas".
The rebel group has accused regime forces of violating ceasefire and said the deal was not performed as "militias and states kill our people".
Jaish al Islam indicated, "Our confrontations with the Assad gangs did not stop, whether in the Ghouta, in Homs, or in Aleppo, and as far as we are concerned, the war effectively did not stop on the ground in the shadow of these violations".
"The regime has been launching a fierce attack on the area for more than four months and we were surprised that after the declaration of the truce by the international community that this attack continued and the Assad forces took new positions in the area," Jaish al Islam said in a statement overnight.
The Jaish al Islam group is one of the important rebel factions fighting Assad regime in western Syria and a key member of the main Saudi-backed opposition council, the High Negotiations Committee.
Jaish al Islam said it faced hard military conditions on one important frontline at Al Maraj outside Damascus, where regime forces have taken ground since the deal came into effect.
The Syrian Network for Human Rights reported it has recorded at least 180 breaches within the first five days after cessation of hostilities deal.