Syrian regime forces have repelled a fierce assault by opposition fighters seeking to reopen their only supply route into Aleppo city, killing at least 29 rebels, a monitor said Sunday.
The offensive sought to push regime forces back from the Castello Road that leads into the opposition-held eastern half of Aleppo city, which is now effectively besieged by government troops.
The Syrian Observatory for Human Rights said 29 fighters from the Islamist Faylaq al-Sham rebel group and Al-Qaeda affiliate Al-Nusra Front were killed in fighting or by mines laid by government troops.
The Britain-based monitor said there were also deaths among government troops, but had no immediate toll.
"The attack has ended and the road remains completely closed," Observatory chief Rami Abdel Rahman said.
The Castello Road was effectively severed by government forces on Thursday when they seized a hilltop within range of the key supply line.
By Saturday, regime soldiers were within 500 metres (yards) of the road and firing on any vehicle trying to use it.
The Observatory said at least one car was targeted on the road early on Sunday, adding that it was unclear if it carried civilians or fighters.
The regime also shelled the road later Sunday, it said.
On Friday, a man and his two sons were killed by regime forces on the road, the monitor said.
An AFP correspondent in eastern Aleppo said opposition factions were preventing civilians from using the route.
Ongoing government artillery fire and barrel bomb attacks were reported in the east of the city early Sunday.
About 200,000 people remain in the eastern part of Aleppo, which has been divided between government and rebel control since shortly after fighting in the city erupted in mid-2012.
President Bashar al-Assad's forces have been trying to cut the Castello Road for more than two years in an attempt to pressure rebel forces in the city.
Their advance on Thursday has left residents of the east cut off, with supplies of basic items including food and fuel starting to run low and fears of a lengthy government siege.
Syria's government has been accused of using sieges to pressure rebel forces, and the UN says nearly 600,000 Syrians live in besieged areas, most surrounded by government forces although rebels also use the tactic.
In the wake of the government advance, rebel forces on Friday retaliated with waves of rocket fire into the regime-held west of Aleppo, killing 45 people, according to Syria's state news agency SANA.
Residents there praised the regime advance but worried about rebel fire into their neighbourhoods.
"We're not leaving home, but even staying at home has become dangerous," 25-year-old Abdel Wahhab Qabbani told AFP.
The latest violence came despite the army's announcement Saturday of a 72-hour extension to a nationwide ceasefire that began Wednesday but has produced little respite.
As well as the fighting in Aleppo, the Observatory said at least four civilians were killed in regime air strikes overnight on the rebel-held town of Douma, east of Damascus.
At a makeshift clinic in the town, medics wiped blood from the back of a small boy who winced as he tried not to cry.
In the central province of Homs, regime air strikes killed eight civilians, including three children from the same family and a further three from another, the Observatory said.
More than 280,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests that sparked a deadly crackdown.
Among the dead have been dozens of journalists, including US reporter Marie Colvin, whose family has filed a lawsuit alleging she was deliberately targeted by Syria's government.
The lawsuit filed in a US court on Saturday claims the Syrian military intercepted Colvin's communications and killed her in Homs city in February 2012 to stop her from covering government atrocities.
The conflict has also seen large parts of the country fall under the control of the Islamic State group, which in 2014 declared a self-styled "caliphate" in territory under its control in Syria and Iraq.
A new analysis by the IHS research group said Sunday that IS group had lost 12 percent of its territory in the two countries so far this year, after losing 14 percent in 2015.
The report said the territorial losses, as well as sinking revenues, would be likely to encourage IS group to pursue "mass casualty attacks" in Iraq, Syria and further afield, including in Europe.