The pan-Arab organisation met in Cairo as fighting that raged in the divided city threatened a complete breakdown of a truce between President Bashar al-Assad's regime and non-jihadist rebels.
More than 280 civilians have been killed in the fighting since April 22, with Assad's regime launching air strikes on the rebel-held east Aleppo while rebels shell the regime-controlled west.
The Arab League said it had decided to "work on bringing all those who participated in and contributed to the brutal attacks against innocent civilians in Aleppo and other Syrian cities to international justice".
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The 22-member bloc denounced the "the Syrian regime's brutal actions against unarmed civilian residents" in Aleppo, calling the attacks "a massacre," in a resolution announced after the meeting.
It also denounced the Islamic State group and "all terrorist groups" which are committing crimes against civilians in Aleppo and other Syrian cities.
The meeting of the bloc's delegates was requested by the Gulf nation of Qatar after Russia announced it would not ask the Syrian government to cease its air strikes on the city.
All member states approved the resolution except Lebanon, which abstained from voting.
More than 270,000 Syrians have been killed in the conflict which began March 2011, and millions have been displaced to other parts in Syria and abroad.