Syrian forces have threatened to mount a "decisive battle" for Aleppo as rebels head towards the city's ancient centre under intense bombardment and strafing from fighter jets.
The pro-government Al Watan newspaper said the Syrian army was bracing itself for a "decisive battle" to clear Aleppo, Syria's largest city, from the rebels.
Activists have claimed for more than a week that the government is gearing up for an all-out offensive on the northern commercial centre, another critical battleground for Bashar al-Assad's government to survive.
In Damascus, armed men appeared to step up guerrilla-like forays in central districts that were once firmly in the government's hands.
The twin fronts reflected the rising stakes for both sides and a possible significant evolution in rebel strategies.
Clashes were reported on Saturday between government forces and rebels around Aleppo's television and radio station.
"It was the most violent shelling of Salaheddin since the outbreak of fighting in Aleppo" on July 20, said the Free Syrian Army's military chief, Colonel Abdel Jabbar al-Oqaidi, according to the Syrian Observatory for Human Rights (SOHR), a London-based rights group opposed to the Assad government.
|Image released by Syria's official SANA news agency purports to show 'terrorists' taken captive by security forces [AFP]
"It is not the first time the army has tried to storm Salaheddin," Oqaidi said.
Syrian television said a large number of "terrorists", the term it uses for the rebels, were killed and wounded after they tried to storm the television and radio station in Aleppo.
Al Jazeera's Ahmed Zeidan, reporting from Aleppo, said: "There has been heavy bombardment in different neighbourhoods in Aleppo: in Shaar, in Bab al-Nayrab and al-Sakhour. We have no information on casualties.
"We have witnessed fighter [jets] bombing heavily in these neighbourhoods."
He said the violence followed the capture by the Free Syrian Army of different sections of older parts of Aleppo on Saturday.
Aleppo is home to 2.5 million people and the fate of Salaheddin district, seen as a gateway for the army, could determine the outcome of a conflict that has already claimed some 18,000 lives.
Syria's official news agency SANA described the Aleppo rebels as "Gulf and Turkish militias", more evidence of the deep regional fissures between Assad and allies such as Iran on one side and countries that back the rebels on the other.
Clashes in Damascus
The government also claimed it had regained full authority over Damascus after driving out rebels from central districts including near Abbassiyyin Square, a major roundabout. But residents reported loud explosions and gunfire echoing from several areas of the capital overnight and early Sunday.
Khaled al-Shami, an activist in Damascus, dismissed as "nonsense" the official reports that rebels were pushed from Damascus. He said rebels are increasingly using a tactic of quick-hit attacks to frustrate security forces and keep the capital unstable.
"The Free Syrian Army does not seek to hold territory in Damascus but rather stage hit-and-run attacks that drain the regime. The rebels are present and strong there," he said.
In other areas of Damascus, government forces raided the district of Qaboon on Sunday, arresting several civilians, the British-based Observatory said, adding that one of the detainees was a 12-year-old boy.
After clashes with rebels in Rokn Eddin on Saturday, the military set up new checkpoints in the neighbourhood of Damascus and in several other parts of the capital.
Elsewhere in the province of Damascus, clashes broke out in Kfar Batna as regime forces shelled that village. The army also shelled Harasta, in the same province.
At Rastan, in the central province of Homs, regime forces pounded rebel positions, said the SOHR.
"Regime forces dropped more than 60 shells on Rastan, at a rate of four to five shells a minute," the watchdog added.
'Acts of brutality'
Syria's unrest has intensified in the past few weeks, with fighting engulfing Damascus and Aleppo for the first time in the 17-month uprising against Assad family rule.
The FSA has launched increasingly bold attacks in the two main cities and established strongholds in relatively central neighbourhoods in recent days.
In-depth coverage of escalating violence across Syria
The rebel army had claimed to have consolidated most of its control in the east of Aleppo, while also maintaining a grip on central neighbourhoods, including Salaheddin and Bab al-Hadid.
Internet and telephone networks in Aleppo were mostly cut for the fourth day on Saturday, hampering attempts by rebels to co-ordinate and forcing them to use couriers to deliver orders.
Meanwhile, Ban Ki-moon, the UN secretary-general, said "acts of brutality" reported in Aleppo could be crimes against humanity.
His comments came before the UN General Assembly adopted a resolution deploring the Security Council for lack of action.
Ban has warned world powers they must overcome their rivalries to put an end to a "proxy war" in Syria.