Armed forces have launched an offensive to seize the besieged Aleppo region from a powerful Islamist group and the Syrian regime.
The offensive is backed by Russian air support, and is the first such operation in the war-torn country.
The military operation comes after an eight-day campaign that began on Friday when the army, backed by the Russian air force, drove out a number of Islamic State (IS) rebels.
The Syrian Observatory for Human Rights, a UK-based group, said the army was aiming to recapture the eastern neighbourhoods of Al-Foua and Maksam, the main urban areas in the eastern part of the city, from the extremist group.
The army also launched an assault on the eastern districts of al-Shayrat and al-Masharra, in addition to the eastern suburbs of al-‘Arish, and al-‘Ada, on the Syrian-Turkish border.
A military source told the AFP news agency that the operation was launched at around 8:00pm local time (21:00 GMT) on Friday.
The source said the operation involved more than 600 troops, including a number that included tanks and artillery, in the south of Aleppo, and was launched in coordination with local commanders.
The operation began in the afternoon on Friday and involved the military units from several branches of the Syrian military, including the army and its air force.
The news agency said that around 200 troops, mostly from the Syrian Arab Army, also participated in the operation.
The official Syrian news agency SANA reported that the offensive was backed by air strikes from the US-led coalition against IS, with air raids from the Russian Air Force.
The SANA news agency also said that the military offensive was part of an offensive by the Syrian government to retake eastern Aleppo from the militant group.
Russian President Vladimir Putin said on Thursday that Russia had been providing air support to the Syrian opposition for more than two months.
The US and UK have been trying to negotiate a political settlement to end the conflict, and the UK is also a key member of the US and EU coalition against the militant groups.
The ceasefire agreement brokered by the US, Russia and Turkey has been widely criticised by both Russia and the West.
Russia has said it will maintain its air support for the Syrian rebels while the US will send troops and weapons to the government.
Russia also announced on Thursday a deal with Turkey for the return of the Black Sea Fleet to the Turkish navy in exchange for the US pulling out its troops from Syria.
“We have decided to restore the Black Seas Fleet to Turkey, which has been under Turkish control for the past 10 years,” the Russian Foreign Ministry said in a statement.