The Local Coordination Committees of Syria said dozens of others were wounded in the city, where the uprising against President Bashar Assad began in March last year, CNN reported.
The London-based Syrian Observatory for Human Rights said those killed in the city included three children and 10 women, The New York Times reported.
In Dara'a, the LCC said: "Several doctors have been detained to prevent them from aiding the wounded amid a state of panic among residents due to the abuses regime forces are committing against the people there."
The group said Assad regime forces had stormed a neighborhood and shelled a mosque and church in Homs, and at least nine people, including the mayor of the Khalidiya neighborhood, were killed.
Meanwhile, U.N. monitors in Syria gathered evidence of the mass killings in Qubeir Wednesday.
Susan Ghosheh, a spokeswoman for the U.N. Supervision Mission in Syria, said in an e-mail: "Inside some of the houses, the walls and floors were splatted with blood. Fire was still burning outside houses, and there was a strong stench of burnt flesh in the air."
Activists said as many as 78 people, half of them women and children, died in Qubeir, about 20 miles from the city of Hama, and the activists blamed government troops and plainclothes militiamen known as shabiha.
Ghosheh said the number of victims hadn't been confirmed and the community was empty so "the observers were not able to talk to anyone who witnessed Wednesday's horrific tragedy."
The Syrian government blamed terrorists for the attack and said nine people died.