BEIRUT — The Syrian government launched new airstrikes Saturday on insurgent-held neighborhoods in Aleppo while rebels shelled government-held parts of the northern city, as a truce in other parts of the country appeared to be holding on its first day.

Contested Aleppo, Syria’s largest city and former commercial center, has been the scene of intense shelling and air raids, killing nearly 250 civilians over the past nine days, according to the Britain-based Syrian Observatory for Human Rights.

A protester holds up a placard during a protest in downtown Beirut, Lebanon, Saturday, April 30, 2016, against Syrian President Bashar Assad's military operations against areas held by insurgents around the country, mostly in the northern city of Aleppo that has been the main point of violence. (AP Photo/Bilal Hussein) The Associated Press

The surge in fighting has caused the collapse of a two-month cease-fire brokered by the U.S. and Russia. It also has raised fears of an all-out government assault on Aleppo.

The International Committee of the Red Cross warned that the intensification of fighting threatens to cause a humanitarian disaster for millions of people. A statement issued late Friday said four medical facilities on both sides of the city were hit earlier that dayl. ICRC appealed to all parties “for an immediate halt in the attacks.”

“There can be no justification for these appalling acts of violence deliberately targeting hospitals and clinics, which are strictly prohibited under international humanitarian law,” said Marianne Gasser, head of the ICRC in Syria.

Friday’s attacks on the medical centers came after government airstrikes damaged a main hospital supported by Doctors Without Borders late Wednesday, killing over 50 people, according to the aid group.

Syrian opposition activists said Saturday’s airstrikes on Aleppo killed four people and wounded many others.

The Observatory and the Local Coordination Committees, another activist-run group, reported more than 20 separate air raids on rebel-held parts of the city, where an estimated 250,000 people remain.

Aleppo was excluded from a brief truce declared by the Syrian army on Friday. The truce went into effect after midnight Saturday in the capital Damascus and its suburbs as well as the coastal province of Latakia. Activists said the truce appeared to be holding in both areas on Saturday.

U.S. Secretary of State John Kerry is leaving for Geneva on Sunday, where he plans to meet the next day with the U.N. envoy to Syria to discuss efforts to halt the violence and increase deliveries of humanitarian aid. Kerry spoke to Russian Foreign Minister Sergey Lavrov on Friday.

Government supporters say Aleppo should not be part of the truce brokered by the U.S. and Russia because al-Qaida’s branch in Syria, known as the Nusra Front, is active there and in nearby areas.

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