The ceasefire has been violated repeatedly in the past two years, with dozens of people killed and injured.
The tent settlement, known as the maram camp, is located just northwest of the provincial capital of Idlib.
The UK-based Syrian Observatory for Human Rightsan opposition war monitor reported that government forces fired about 30 rockets into rebel-held areas, including the Maram camp on Sunday morning, killing six and injuring 15. It said that the dead included two children and a woman.
Other opposition activists also reported that six people were killed and more than 30 injured.
The pro-government Sham FM radio station said Syrian government forces shelled positions of the al-Qaida-affiliated Hayat Tahrir al-Sham group, the most powerful militant group in Idlib. It said Syrian and Russian warplanes also attacked the areas.
The conflict in Syria erupted in March 2011 and has since killed hundreds of thousands of people, displaced half of the pre-war population of 23 million and devastated large parts of Syria.