Syrian rebels fought fierce battles with regime forces in a failed bid to reopen their only supply route into Aleppo city overnight, losing at least 29 combatants, a monitor said Sunday.
The assault 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," said Observatory chief Rami Abdel Rahman.
The Castello Road was effectively severed by government forces on Thursday when they seized a hilltop within firing range of the key supply route.
By Saturday, regime soldiers were within 500 metres (yards) of the road and firing on any vehicle attempting to use it.
An AFP correspondent in the eastern side of the city said opposition factions were preventing civilians from using the road.
Ongoing government artillery fire and barrel bomb attacks were reported to the east of the city on Sunday morning.
The 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 in fighting.
The Observatory said at least one car had been targeted on the Castello Road early on Sunday morning, adding it was unclear if it was carrying civilians or fighters.
On Friday, a man and his two sons were killed by regime forces while using the road, according to the monitor.
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 route for more than two years in a bid 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 siege tactics 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 method.
More than 280,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.