Syrian troops and rebels fought pitched battles near an intelligence headquarters in Aleppo, a watchdog said, as a military offensive in Syria's commercial capital raged into a fourth day.The fighting erupted when rebels launched an assault before dawn on Tuesday on the powerful air force intelligence branch in Aleppo's Zahraa district, the British-based Syrian Observatory for Human Rights said. Fighting was continuing into the day.Also Tuesday, rebels armed with rocket propelled grenades attacked Aleppo's main military court as well as a police station and a branch of the ruling Baath Party in the city's southern Salhin district, the Observatory said.Meanwhile, the neighbourhoods of Firdoss, Al-Mashhad and Ansari were bombarded through the night by government troops, the watchdog said.The Syrian army said on Monday it had overrun part of the city's rebel-held Salaheddin district, which sits in the southwest in the face of the government advance, but that claim was denied by a rebel Free Syrian Army commander."The Syrian army took control of part of Salaheddin district and continues its offensive," a security source in Damascus said.But Colonel Abdel Jabbar al-Oqaidi, head of the rebel military council in Aleppo, insisted government troops had "not progressed one metre"."We launched a new assault from Salaheddin during the night, and we destroyed four tanks," the rebel commander said by phone.Hospitals and makeshift clinics in rebel-held eastern neighbourhoods were filling up with casualties from a week of fighting in the city, a commercial hub drawn into the 16-month-long revolt against President Bashar al-Assad."Some days we get around 30, 40 people, not including the bodies," said a young medic in one clinic. "A few days ago we got 30 injured and maybe 20 corpses, but half of those bodies were ripped to pieces. We can't figure out who they are."Omar Khashram, an Al Jazeera reporter, was injured by shrapnel when a mortar round fell near the car he was riding in.Other Al Jazeera journalists in the same car were unhurt. Khashram was hit in areas unprotected by his flak jacket and was evacuated safely to Turkey. The Syrian Observatory for Human Rights, an activist group in London, said 40 people, 30 of them civilians, were killed in Syria on Monday, and two rebel fighters died in Salaheddin.