Syrian rescue workers, firefighters and citizens walk on a street following reported bombings by government forces on a market on the rebel held al-Shaar district of the northern Syrian city of Aleppo on September 21, 2015.

Heavy bombardment by forces loyal to Syrian President Bashar al-Assad killed at least 18 civilians Monday in a residential district of the northern city of Aleppo, a monitor said.

“Regime forces fired on the Al-Shaar neighborhood in Aleppo city’s east, which is controlled by the opposition, and killed at least 18 civilians,” said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

“A surface-to-surface missile hit the Al-Shaar neighborhood. People started gathering, and that’s when the army fired more missiles at the same area,” he said.

Abdel Rahman said dozens of people were wounded and others were still trapped under the rubble.

Aleppo was once Syria’s economic powerhouse, but it has been devastated by fighting since 2012.

The city is now divided between government control in the west and opposition control in the east.

Much of Aleppo has been left in ruins as regime forces carry out aerial attacks and rebels retaliate, despite criticism of both sides from humanitarian organizations.