At least 66 more civilians were killed Wednesday across Syria in the latest fighting of the 15-month uprising against President Bashar al-Assad's government, opposition activists said Thursday.

The dead included 17 in the suburbs of the capital, Damascus, according to the Local Coordination Committees of Syria, an opposition network. Most of those were killed in the suburb of Douma, which the LCCS said was being shelled by government troops.

Another 24 people were in Hama and seven in Daraa, cities that were the scenes of previous fighting between anti-government protesters and Syrian police and troops. The remainder of the fatalities were scattered across a number of other cities, including Idlib and Homs, where the Red Cross said fighting between government forces and armed opposition groups continued in several neighborhoods

"Hundreds of civilians are stuck in the old city of Homs, unable to leave and find refuge in safer areas, because of the ongoing armed confrontations," Béatrice Mégevand-Roggo, the regional operations chief for the International Committee of the Red Cross, said in a written statement Wednesday.

"It is critical that the ICRC and the Syrian Arab Red Crescent be immediately given safe and unhindered access to those in need of lifesaving assistance."

Former U.S. soldier aids Syria's wounded

Syria's government launched a crackdown on anti-government protests in March 2011, amid the "Arab Spring" revolts that forced several neighboring regimes from power.

Opposition leaders say more than 13,000 people have been killed since then, and the head of a U.N. monitoring mission told reporters Tuesday that the conflict has only gotten worse since a cease-fire agreement in April.

Syria's government, meanwhile, says it is battling armed terrorist groups.

CNN cannot independently verify government and opposition claims of casualties because access to Syria by international journalists has been severely curtailed.