Syrian opposition rebels heavily shelled regime areas in the northern city of Aleppo late Friday, killing at least 25 civilians, including four children, after Syrian forces intensified shelling and airstrikes on rebel-held areas in the city, a monitoring group said.
More than 120 people were also wounded when shells fell on al-Furqan, al-Martini and al-Mashrika neigbourhoods which are under the control of the Bashar al-Assad regime, the Britain-based Syrian Observatory for Human Rights said.
The watchdog said a number of people were severely wounded in the shelling and the death toll was expected to increase.
Aleppo, Syria's commercial hub, has been divided between al-Assad's forces in the west and rebels in the east since fighting erupted for the control of the city in mid-2012.
Earlier, at least 12 civilians, including six children, were killed in overnight strikes on rebel-controlled areas in Aleppo, the Observatory said.
The violence took place despite a nationwide truce that was announced on Wednesday. The Syrian army said the three-day "regime of calm" had gone into effect and would continue until midnight (2100 GMT Friday).
The ceasefire coincided with the start of the Eid al-Fitr holiday marking the end of Islam's holy month of Ramadan.
Regime warplanes Friday intensified their air bombardment near the strategic Castello Road, the only supply route to the rebel-held areas in Aleppo.
Regime forces are now only 400 meters from the road, pro-Syrian regime Lebanese al-Maydeen Television said.
A rebel fighter said government forces, backed by Russian airpower, had carried out at least 20 airstrikes on Castello Road.
"The regime is aiming at cutting the road to impose a kind of starvation war on the remaining people of Aleppo," he told dpa via Skype.
There are between 250,000 and 300,000 people living in rebel-held areas of Aleppo, according to the Observatory.
On Thursday, forces loyal to al-Assad cut off Castello Road and seized parts of the Mallah Farms area that overlooks the route.
Sources in the Syrian Free Army say that rebels have a substitute road that runs through trees in the area. But the alternative route is now unsafe because of regime forces' direct firepower, they told dpa.
Should government forces dislodge the opposition from the area around Aleppo, they are expected to impose a siege on the city.
Al-Assad's forces have made territorial gains against rebels since September, when Russia started an air campaign in Syria in support of the regime. There has since been an increase in civilian deaths.
Separately at least 23 civilians, including women and children, were killed in airstrikes by unidentified warplanes in the Idlib province in north-western Syria on Friday, the Observatory said.
Around 40 others were injured in the strikes on the rebel-held village of Darkoush in Idlib near the Turkish border, it added.
Darkoush is controlled mainly by Syria's al-Qaeda branch, al-Nusra Front.
Later on Friday, unidentified jets struck other rebel-held areas in the north-western parts of Idlib, the Observatory said, mentioning unspecified civilian casualties.