Rockets fired by insurgents killed 19 people and hit a hospital in government-held parts of Aleppo city on Tuesday, the Syrian Observatory for Human Rights said on Tuesday.
State-run Syrian news channel Ikhbariya said three women were killed and 17 more people wounded at the al-Dabit maternity clinic.
The Syrian army said in a statement the attack was part of a widespread assault by insurgent groups in Aleppo on Tuesday and that it was responding.
The army statement said the attack was at "a time when international and local efforts are being made to shore-up the (cessation of hostilities agreement) and to implement...calm in Aleppo".
The Observatory said the hospital had been heavily damaged.
In rebel-held parts of Aleppo, the Observatory said there had been three air strikes, citing information of an unconfirmed number of people killed.
The Observatory said 279 civilians have been killed in Aleppo by bombardments since April 22, with 155 of them killed in opposition-held areas, and 124 killed in government-held districts.