Story highlights At least 38 civilians killed in two days in western Aleppo, human rights group says

Rebels trying to expand territory they captured Friday from government forces

(CNN) Groups fighting the Syrian regime in Aleppo on Sunday intensified attacks on the government-controlled western section of the city.

Jaish al Fateh, an umbrella group that includes multiple rebel and Islamist factions, issued a statement Sunday declaring "military zones" in several neighborhoods in western Aleppo, the Aleppo Media Center, or AMC, activist group said.

Jaish al Fateh advised civilians to stay home or take refuge in basement shelters.

At least 38 civilians, including 14 children, have been killed in the last two days by rebel shelling of government-held parts of Aleppo, said the Syrian Observatory for Human Rights, or SOHR. At least 250 other people were injured.

Rebels allied with jihadist groups on Sunday tried to expand their toehold of territory on the southwestern outskirts, which they captured in a Friday offensive against the regime.

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