Regime air strikes drops "barrel bombs" on rebel districts, according to the Syrian Observatory for Human Rights. The crude and imprecise bombs are made of TNT packed into oil drums that are dropped from the air.
Following are key dates in the battle for Syria's Aleppo where fierce fighting resumed on Wednesday in a blow to hopes for the peaceful evacuation of the last rebel-held areas.
- April-May, 2011: Thousands of students demonstrate in Aleppo, a northern city that had been spared the violent protests that erupted elsewhere in the country. The protests are swiftly crushed by security forces and rival students who back the regime of President Bashar al-Assad.
- July 20, 2012: Fierce fighting breaks out between the army and rebels of the Free Syrian Army, a group of armed civilians and army deserters, in several city districts.
- In August the same year, troops backed by heavy artillery and warplanes secure central Christian neighbourhoods after a two-week offensive.
After that, the city is divided between loyalist districts in the west, where around 1.2 million people live, and rebel-controlled areas in the east with a population of more than 250,000.
- December 15, 2013: Regime air strikes drops "barrel bombs" on rebel districts, according to the Syrian Observatory for Human Rights. The crude and imprecise bombs are made of TNT packed into oil drums that are dropped from the air.
Rebel tactics include firing rockets on government-held areas of the city.
- September 2015: Russia comes to the aid of Assad's government, launching air strikes on Syria.
- February 1, 2016: The regime launches an offensive against rebels in Aleppo province, backed by Hezbollah fighters and Russian aircraft.
- July-August: Government forces cut the rebel's last supply route into Aleppo, effectively placing east Aleppo under regime siege, with inhabitants hit by food and petrol shortages. Rebels make several attempts to break the siege, but aid does not get through.
- September 22: After the end of a one-week ceasefire brokered by Russia and the United States, the Syrian army announces a major offensive to retake all rebel-held areas.
- October 5: The United Nations declares Aleppo's eastern districts "besieged".
- November 15: After almost a month of relative respite, regime forces, initially with Russian air support, launch a new assault to recapture the entire city. Rebel areas come under the heaviest bombardment for two years, with barrel bombs, shells and rockets.
- November 26: The government announces that the district of Masaken Hanano -- the largest rebel zone -- has been recaptured.
- December 6: Eight more districts in eastern Aleppo, including the strategic Shaar neighbourhood, fall into regime hands.
- December 7: Rebels make a highly symbolic retreat from the Old City.
- December 12: The army captures the Sheikh Saeed district in the southeast, giving it control of 90 percent of the onetime rebel sector.
- December 13: The guns fall silent after regime-backer Russia and rebel-supporter Turkey broker an agreement for a ceasefire and the evacuation of thousands of civilians and fighters from the last remaining rebel districts.
- December 14: Fierce fighting resumes after hours of calm, as the evacuation agreement is put on hold with the rival sides trading blame.