At least 50 people were Sunday killed across Syria, where opposition activists said President Bashar al-Assad's troops had stepped up attacks on pro-rebel areas, dpa reported.
The bulk of the deaths occurred in restive areas near the capital Damascus and the northern city of Aleppo, said the opposition Syrian Observatory for Human Rights.
Sounds of exploding shells and machine gun fire could be heard across Damascus, as fighting between government troops and rebels raged in the north-eastern suburb of Harasta, added the London-based organization.
The watchdog said helicopter gunships had pounded the opposition bastions of Hanano and Sakhur in the north of Aleppo and the district of Bustan al-Qasr in the south-western part of the embattled city. Rebels meanwhile claimed they had regained "full control" of the neighbourhood of Salaheddin in the south of Aleppo from al-Assad's troops.
Both sides have been fighting in Aleppo, Syria's biggest city and commercial hub, for more than two months. Syrian troops shelled the restive town of al-Rastan in the central province of Homs, said the observatory.
The violence coincided with the presence of United Nations-Arab League envoy Lakhdar Brahimi in Damascus, where he met al-Assad on Saturday and warned that the conflict in Syria posed a global threat.