Syrian army helicopters bombed positions held Saturday by insurgents in the center of Aleppo and armored units took up positions to take full control of the biggest city in northern Syria.
Turkey, concerned about the development of the conflict on its borders, has called for new international initiatives to end the fighting.
The Syrian Observatory of Human Rights (SOHR) reported that government helicopters had attacked the neighborhood of Salaheddin in Aleppo. Heavy fighting also took place at the entrance to the Sakhour neighborhood, added the NGO.
An opposition activist said he saw tanks and armored troop carriers move into the neighborhood of Salaheddin.
The international community is worried that the battle of Aleppo will result in massacres of civilians and the conflict will spread other countries in the region.
A dozen of people were injured last night in Tripoli, the main city in northern Lebanon, during firefights between Sunni and Alawite gunmen. The army has had to intervene.
On one side, Bab al-Tabbaneh, a Sunni stronghold whose residents opposed the Syrian regime. The other district, Jabal Mohsen is an Alawite area, which supports Syrian President Bashar al-Assad.
Since mid-May, about 40 people died in the fighting in Tripoli over the Syrian crisis. The gunmen use automatic weapons and rockets.
For many military experts, Assad's forces, because of their material superiority, are able to control urban areas, including Aleppo and Damascus, but could find themselves on the defensive in rural areas.
On the night between Friday and Saturday, three rebel fighters were killed in the fighting in Aleppo. All in all on Friday, the violence left 160 dead across the country, said the NGO.
Clashes were also reported Saturday in Deraa, the cradle of the revolt in the south, in Homs and Hama.
On Friday night, Turkish Prime Minister Recep Tayyip Erdogan, once a close ally to Assad, said that the international community should do something about the worsening situation in Aleppo and Damascus' threat to use its arsenal of chemical arms in case of foreign aggression.
"There are reinforcements (of the Syrian army) in Aleppo, and recent statements on the use of weapons of mass destruction are the elements to which we can not remain mere observers or spectators," he said in London at a joint press conference with British Prime Minister, David Cameron.