Dozens of people are reported to have been killed in fierce clashes between rebel groups and government forces in the divided Syrian city of Aleppo.
Rebels advanced into government-held western districts overnight but were pushed back by the morning, the Syrian Observatory for Human Rights said.
The battle was the most intense in Aleppo for more than a year, it added.
The violence comes as the US and Russia attempt to include the city in a temporary truce in place elsewhere.
Russian Foreign Minister Sergei Lavrov said on Tuesday that he expected a decision very soon on extending the “regime of calm” declared on Saturday by the government around Damascus and in Latakia province.
The truce expired at midnight in the capital, and on Wednesday activists in the rebel-held eastern Ghouta region reported fresh clashes and air strikes.
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A surge in fighting in Aleppo in the past two weeks has killed almost 300 people and left a nine-week nationwide cessation of hostilities close to collapse.
A coalition of rebel groups fighting under the name “Fatah Halab” (Aleppo Conquest) launched the assault on the government’s defensive lines in the west of the city on Tuesday by exploding a tunnel bomb, the AFP news agency reported.
There were intense gun battles, air strikes and artillery attacks throughout the night, and clashes were still going on intermittently on Wednesday.
There were conflicting accounts of the outcome of the battle.
The Syrian Observatory, a UK-based monitoring group, reported that the rebels initially made gains, but were eventually driven back by government troops, backed by fighters from Lebanon’s Hezbollah movement.
A rebel fighter told the Reuters news agency that some ground had been captured from the government side, while a military source said the attack was repelled.
The rebel said about 40 pro-government fighters and 10 rebels had been killed, according to Reuters. The military source denied there were heavy army casualties, but said dozens of civilians and many rebels had been killed.
State media said government troops had repelled an attack on a government-controlled suburb, and that three civilians had been killed by rebel rocket fire.