Intense fighting has continued around the Syrian city of Aleppo, where a rebel offensive is trying to break a government siege of rebel-held areas.
Over the weekend, the rebels tried to reconnect an encircled area in the east with insurgent territory in the west.
They set off a huge tunnel bomb underneath army positions in the strategic Ramouseh district.
The army has been fighting back with the help of Russian air strikes to stop the rebels breaking through.
Around a quarter of a million civilians are living under siege in rebel-held areas since government forces cut them off last month.
"We are now overlooking the Ramousah area but Russian jets are intensifying their bombing, which is holding us back from moving quickly," a rebel commander told Reuters news agency.
Another rebel source told Reuters that about 10,000 troops, at least 95 tanks and several hundred rocket launchers had been deployed for what he described as the "great epic battle of Aleppo".
The source said scores of suicide bombers had also been prepared to drive explosive-laden military vehicles into army posts.
UK-based monitor the Syrian Observatory for Human Rights described the rebel offensive as the largest so far, involving fighting across the divided city's main battle fronts.
