BEIRUT (AP) — Syrian warplanes pounded a strategic northern city with three airstrikes Tuesday as ground troops pushed forward to recapture the area recently taken by rebels, activists said.

The fighting over Maaret al-Numan, which sits along the main highway that connects Aleppo and Damascus, comes as the regime intensifies efforts to retake the area that was seized by rebels earlier this month.

Their presence has disrupted the regime’s ability to send supplies and reinforcements to Aleppo, where regime forces are bogged down in a bloody fight for control of the country’s largest city.

Syrian troops have been fighting against rebels in Aleppo since July and rebel advances over the past week have added urgency to the battle.

The Britain-based Syrian Observatory for Human Rights said four people, including three young girls, were killed in the air raids on Maaret al-Numan.

Another activist group, the Local Coordination Committees put the death toll from the airstrikes and ground fire at 19. Discrepancies in casualty tolls are frequent because of restrictions on independent reporting and the chaos on the ground.

The LCC and the Observatory reported air raids on several suburbs of Damascus including the restive areas of Arbeen, Zamalka and Douma.

Tuesday’s airstrikes came a day after activists reported the most widespread bombing in a single day since Syria’s 19-month crisis began. Maaret al-Numan was among the hardest hit on Monday as well.

Rami Abdul-Rahman, who heads the Observatory, said ground troops were fighting rebels on the southern edge of the city, 80 kilometers (50 miles) southwest of Aleppo.

"The regime wants to recapture Maaret al-Numan because it links Damascus with Aleppo," Abdul-Rahman said referring to Syria’s two largest cities. "It is a very strategic city."

Anti-regime activist say more than 35,000 people have been killed since the uprising against President Bashar Assad’s regime started in March 2011.

In Damascus, meanwhile, Syrian troops and rebels clashed in the Palestinian refugee camp of Yarmouk, activists said. The LCC and the Observatory said the fighting broke out after midnight, but they had no word on casualties.

Palestinian refugees in Syria tried to stay on the sidelines when the uprising began. But many Palestinian youths have joined the fight as they became enraged by mounting violence and moved by Arab Spring calls for greater freedoms.