Activists say Syrian troops are shelling restless suburbs of Damascus and rebel-held areas in the central city of Homs.
The rural district of Houla, where 108 people were massacred last week, is in the province of Homs.
Western nations have expelled Syrian diplomats in a coordinated move to protest the massacre, which survivors say was largely carried out by pro-regime gunmen.
The Syrian government has said it will conclude on Wednesday its own investigation into the killings. It is not clear whether the results will be made public.
Satellite images released by Human Rights Watch