A rebel assault to break the siege of Syria's Aleppo slowed Monday amid fierce resistance from regime forces, as the UN said it was "appalled" by opposition fire on civilians.
Rebels launched a major assault on Friday, backed by car bombs and salvos of rockets, to break through government lines and reach the 250,000 people besieged in the city's east.
Aleppo has been hit by some of the worst violence in Syria's five-year conflict, turning the once-bustling economic hub into a divided and bombed-out symbol of the brutal war.
Since Friday, opposition factions allied with jihadists have amassed on Aleppo's western outskirts in a bid to end the regime's three-month encirclement of the city's eastern districts.
While they scored an initial advance, the offensive has since slowed, according to the Syrian Observatory for Human Rights, a Britain-based monitor.
"Since Sunday, the regime has been taking the initiative and the clashes are less intense," Observatory head Rami Abdel Rahman said on Monday.
"The only thing that has been accomplished is partial control over Dahiyet al-Assad," a neighbourhood on Aleppo's western outskirts that rebels entered on Friday, he said.
Regime and Russian air strikes were hitting the battlefronts on the city's edges, but with less intensity than in previous days.
"The momentum of the rebel offensive slowed after failing to take control of the '3000' apartment block and the military complex," a pro-regime military source said, referring to two built-up areas southwest of Aleppo.
In a new toll on Monday, the Observatory said a total of 61 regime fighters and allied militiamen were killed in the assault, as well as 72 Syrian rebels.
Heavy rebel rocket fire since Friday has killed 48 civilians, including 17 children, the monitor said.
According to Syrian state news agency SANA, three civilians were killed in rebel fire on Aleppo Monday.
UN peace envoy Staffan de Mistura said the high civilian toll raised deep concern.
In a statement on Sunday, his office said he was "appalled and shocked by the high number of rockets" fired by rebels.
"Those who argue that this is meant to relieve the siege of eastern Aleppo should be reminded that nothing justifies the use of disproportionate and indiscriminate weapons, including heavy ones, on civilian areas and it could amount to war crimes," he said.
De Mistura said "civilians of both sides of Aleppo have suffered enough due to futile but lethal attempts of subduing the city."
Aleppo's front line runs through the heart of the city, dividing rebels in the east from government forces in the west.
Rebel groups have pledged to push east from Dahiyet al-Assad to Hamdaniyeh, a regime-controlled neighbourhood directly adjacent to the besieged eastern districts.
Sarab Abu Abdo, a rebel commander in the Army of Conquest alliance, said fighting was "ongoing with light weapons" on Monday.
"We seized three blocks of the 3000 apartment complex, but the regime still controls most of it," Abu Abdo told AFP.
He said regime forces had tried twice to overrun Minyan, a village west of Aleppo captured by rebels on Saturday, but failed.
An AFP correspondent saw about a dozen civilians, including women and children, fleeing Dahiyet al-Assad on Sunday.
They brought belongings stuffed into plastic bags, hoisting them on top of their heads or dragging them along the dusty road.
Syria's conflict broke out in March 2011 with widespread protests calling for the ouster of President Bashar al-Assad.
But it has since evolved into a complex, multi-front war pitting regime forces, rebels, Kurds, and jihadists against each other.
In Daraa, the southern province where demonstrations against Assad first erupted, a massive regime ambush left at least 34 rebels and allied jihadists dead.
The Observatory said the attack took place late Sunday night as the opposition fighters were preparing for a an attack on nearby government positions.