BEIRUT — Syrian warplanes have killed dozens of civilians, including more than 20 children, in an intensifying campaign of anti-insurgency airstrikes across the country over the past few days, bombing some targets as families were congregating outside to enjoy a sunny break from prolonged winter storms, activists and international medical aid workers said Monday.

Their version of events was disputed by the Syrian government, which said through the official news agency that the airstrikes had made great progress against what it called armed terrorists fighting against President Bashar Assad.