Syrian forces have renewed their assault on the northern city of Aleppo, firing from helicopter gunships on rebel-held areas.
The US state department has said it fears Syrian government forces are preparing to carry out a massacre.
The pro-government al-Watan newspaper has warned that the mother of all battles is about to start.
Rebels in Aleppo, Syria's most populous city, have been stockpiling ammunition and medical supplies in preparation.
Syrian troops fired from helicopter gunships on south-western neighbourhoods of Aleppo, the Syrian Observatory for Human Rights told the AFP news agency.
