BEIRUT, Lebanon — Bombs from airstrikes hit three hospitals on Wednesday in the rebel-held side of Aleppo, Syria, including a pediatrics center supported by the United Nations, in what aid providers and opposition activists called a new atrocity in the fighting that has ravaged the city.

The Middle East regional office of Unicef, the United Nations Children’s Fund, said in a statement that the attacks happened within a space of three hours on al-Bayan and al-Hakeem hospitals and the Abdulhadi Fares clinic.

Unicef provided no details on casualties, damage or who was responsible, but it said the attack was the second on al-Hakeem hospital, which it helps operate.

Others said that at least 10 civilians were killed in the bombings, including children, and that many others were wounded. Activist groups blamed Syrian military forces. Insurgents have no aircraft, which are used to conduct such bombings.