For the first time in the 17-month-old uprising against President Bashar al-Assad's rule, Syria's two largest cities are simultaneous battlegrounds.
Both are crucial prizes in an increasingly brutal struggle that has eluded all attempts at a diplomatic solution and risks igniting a wider conflagration.
In Aleppo's Salaheddine district, rebels from the Free Syrian Army (FSA) hid in alleyways, dodging Syrian army bullets and tank rounds that hit one building.
"There is one helicopter and we're hearing two explosions every minute," said a journalist contacted inside the city by satellite phone.
A Syrian activist also confirmed that earlier yesterday rebel fighters tried to extend their area of control from the Salaheddine district, where the most intense fighting has been focused, north to the area around the television and radio station.
"The Free Syrian Army pushed from Salaheddine to al-Adhamiya where they clashed this morning with Syrian troops. But they had to retreat," said the activist, who identified himself as Barraa al-Halabi.
A 19-year-old fighter called Mu'awiya al-Halabi, who was at the scene, said army snipers surrounded the station and targeted the rebels.
"We were inside it for a few hours after clashes with the Syrian army but they sent snipers and surrounded the TV station, and as soon as morning came, the army started shooting. One of our fighters was martyred and four were wounded."
Black smoke rose from Salaheddine, seen as a gateway for the Syrian army into the city of 2.5 million. Its fate could determine the outcome of a war that has claimed 18,000 lives.
Another rebel commander in Aleppo expected a Syrian army attack on rebels "within days", echoing Herve Ladsous, head of the United Nation's peacekeeping department, who said there had been a "considerable buildup of military means".
"We have information that the Syrian army is planning a strong offensive against Aleppo. We know they are planning to attack the city using tanks and aircraft, shooting at us for three to four days and they plan to take the city," said Colonel Abdel-Jabbar al-Oqaidi.
Faced with the Syrian army's superior firepower, Oqaidi said the rebels were counting on mass defections by government soldiers once the offensive started.
"At the moment the soldiers cannot leave their bases and they are too afraid to defect. Once they are inside our city they will take off their uniforms and join us," he said.
In the capital, Damascus, a resident in the Adawi neighbourhood just north of the central Old City yesterday reported loud explosions and jets flying overhead.
"The bombardment has been continuous since 7am in Tadamun district. It hasn't stopped for a moment," said the Adawi resident.
Syrian soldiers were on the streets, telling people to stay indoors because of clashes in the nearby Basateen area. On Friday, they stormed Tadamun, the last rebel stronghold in the city.
The escalation in the fighting comes as efforts to find a diplomatic solution continue to be elusive.
Former UN Secretary General Kofi Annan, who is quitting as international peace envoy for Syria, said on Thursday that Assad should step down. He urged Syrian allies Russia, China and Iran to persuade Assad to embrace political transition.
Annan complained of "finger pointing" at the United Nations while bloodshed in Syria went on.
Yesterday, China hit back at criticism of its stance over the crisis after a vote at the United Nations which overwhelmingly condemned the Syrian government, repeating Beijing's position that outside interference will not help.
"Those countries which have made unfounded criticism about China's position on Syria ... have, in pursuit of their own geopolitical interests in Syria, tried to hinder or undermine the political settlement process and are trying to shift responsibility for the difficulties onto other countries," said Wang Kejian of the Chinese Foreign Ministry.
Russia and China voted down a Security Council resolution on Syria last month, the third time they have vetoed resolutions meant to isolate Assad and end the conflict.