Damascus, Oct 27 (IANS): At least five people were killed Monday in rebel attacks on populated areas in the northwestern Syrian province of Aleppo and in the capital, Damascus, according to media.

Rebels fired mortar shells on the al-Hamadaniyeh neighbourhood in Aleppo, killing four people and injuring 17 others, Xinhua reported citing the state news agency SANA, noting that most of the victims were children.

Also Monday, one person was killed and seven others wounded when an explosive device attached on a bicycle went off in the famous al-Hamidiyeh marketplace in the old city of Damascus.

Firing mortar shells and staging blasts are among the tactics used by rebels throughout the Syrian crisis to destabilise government-controlled areas, with Damascus receiving the lion's share of almost daily mortar shelling by rebels in the suburbs who could not otherwise reach the heavily-fortified city.

Such mortars often explode in residential areas, killing and injuring many.

Meanwhile, the Syrian Observatory for Human Rights, a London- based monitoring group, said that more than 600 Syrian airstrikes were carried out over the past seven days against several rebel-held areas across the war-torn country, adding that around 500 people and fighters were killed as a result of the intensified airstrikes.

The observatory's account could not be verified independently.

Other activists say the Syrian forces are intensifying airstrikes against rebel-held areas across Syria to hasten the destruction of some rebel groups while the US-led coalition is carrying out its air raids on Islamic State militants in areas in northern Syria.

More than three years' conflict in Syria has killed over 190,000 people and displaced millions of others.