At least 18 civilians including four children were killed and 120 others wounded on Friday in rebel shelling of regime-held districts of Syria's Aleppo, the Syrian Observatory for Human Rights said.

The shelling comes as a 72-hour nationwide ceasefire -- announced by the army to mark the end of the holy month of Ramadan -- is due to end at midnight (2100 GMT Friday).

Fighting has continued since the truce was announced on Wednesday, particularly in and around Aleppo, with deaths on both sides of the divided city.