BEIRUT – Rebels backed by captured tanks launched a fresh offensive on a government complex housing a police academy near the northern city of Aleppo on Sunday, while the government hit back with airstrikes to try to protect the strategic installation, activists said.

If rebels capture the complex on the outskirts of Aleppo, it would mark another setback for President Bashar Assad. In recent weeks, his regime has lost control of key infrastructure in the northeast including a hydroelectric dam, a major oil field and two army bases along the road linking Aleppo with the airport to its east.

Rebels also have been hitting the heart of Damascus with occasional mortars shells or bombings, posing a stiff challenge to the regime in its seat of power.