Syria's rebel-held Idlib province came under heavy bombardment on Sunday as rebels and pro-government forces battled for control of the nearby city of Aleppo, activists said.
Much of the fighting has been marked by indiscriminate shelling, missile attacks, and aerial bombardment, killing scores of civilians across Idlib and Aleppo. The rebels do not have an air force.
The Britain-based Syrian Observatory for Human Rights reported 26 air strikes on Sunday across Idlib, one of the last remaining opposition bastions.
Observatory head Rami Abdurrahman said Russian and government air strikes on the north-western province have intensified since rebels launched a campaign from Idlib to break a government siege of Aleppo's opposition districts on July 31.
The strikes have killed 122 civilians, he said.
Another 327 civilians, including 126 children, have been killed in fighting in Aleppo province, according to the Observatory, which monitors both sides of the conflict and gathers information from a network of activists inside Syria.
The toll includes 126 people killed by rebel shelling of government-held parts of Aleppo city.
Tens of thousands of Syrians displaced from Aleppo have found refuge in Idlib, home to a pre-war population of 1.5 million.
The Local Co-ordination Committees, an activist network, said Russian jets struck the towns of Jisr al-Shaghour and Binnish, while the Observatory reported strikes on the provincial capital, Idlib. It was unclear how the activists identified the planes.
Aleppo, once Syria's largest city and commercial capital, is now the focal point of the civil war and the only major city where the opposition to President Bashar Assad still has a foothold.
The rebel campaign, spearheaded by ultraconservative factions including the al Qaida-linked Jaish Fatah al-Sham, formerly known as the Nusra Front, has drawn manpower from Idlib, some 30 kilometres (19 miles) to the west.
A spokesman for the ultraconservative Ahrar al-Sham faction confirmed that the rebels were drawing recruits from Idlib.
"The battle for Aleppo concerns all of Syria," said Abu Khaled, who gave only his nom de guerre.
At least 97 rebel fighters from Idlib have died in combat in Aleppo since July 31, according to Mr Abdurrahman.
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Aleppo is still home to some two million people, most of whom live in the government-controlled western districts.
On Sunday evening, rebels opened a new front, sending a truck bomb into the western Zahraa neighbourhood, according to the Twitter account of the Islamic Front, one of the factions fighting for the city.
The Observatory reported fighting in the city's western and southern districts.
To the east, a Kurdish-led force known as the Syria Democratic Forces (SDF) drove the Islamic State group out of the strategic town of Manbij on Saturday and announced a new campaign against al-Bab, a nearby town held by the extremists.
The US has provided the SDF with air cover and American special forces are advising them on the ground.
Moscow has been waging an air campaign in support of government forces for nearly a year.
Russia's military said six long-range Tu-22M3 bombers that took off from Russian territory carried out strikes on IS near the eastern Syrian city of Deir el-Zour on Sunday. It made no mention of any strikes in Idlib.
Elsewhere in Syria, rebels and government forces battled around a major power plant in the central Hama province.
State media reported that rebels inflicted heavy damage to the Zaara generating station, while an opposition media activist in the nearby town of Aqrab said the power plant was not targeted.
Obeida al-Hamawi, of the activist-run Hama Media Centre, said government forces had launched an assault from positions near the plant to retake the village of Zaara, captured by rebels earlier this year.
He said electricity was still being supplied to the area.
The Observatory reported heavy clashes in the area. In the south, rockets set two apartment blocks on fire in a besieged, opposition-held suburb of Damascus.
The local council in Daraya accused the government of using incendiary weapons, and posted videos showing volunteers transporting water tanks on tractors to help firefighters battle the blaze.
The Observatory also reported a government rocket attack on the suburb.
Following an international appeal, the Syrian Arab Red Crescent rescued a 10-year-old girl from the besieged Damascus suburb of Madaya to receive urgent care after activists say she was shot by a pro-government sniper on August 2.
Syrian state media said "terrorists" shot Ghinwa Qweider and then prevented the evacuation.
Amnesty International said the government held up the request for nearly two weeks.