Syrian airstrikes and artillery targeted Douma, a rebel-held town not far from Damascus, and parts of Aleppo on Saturday, in a series of deadly attacks which killed at least 25 people so far, according to the Syrian Observatory for Human Rights (SOHR).
Escalating fighting around Damascus, Aleppo and other towns threatens to shatter the already fragile ceasefire deal between the regime and rebels, which was brokered in late February.
At least twelve civilians were killed in airstrikes in Aleppo. Zouhir al Shimale, a local journalist, told Al Jazeera that mainly civilian areas were being hit by strikes.
"People were near or at the mosques when the strikes hit," Shimale said, estimating that at least 30 civilians were injured near Bustan al Qasr, the last remaining crossing point between rebel and regime-held sides of Aleppo.
SOHR said that 13 people died during shelling that targeted Douma, east of Damascus, a death toll which is expected to rise because of the high number of critical injuries incurred during the attacks. According to Syrian Civil Defense, a humanitarian group, women and children are among those killed during the shelling, which reportedly hit residential areas and busy markets.
Douma has regularly been a flashpoint for violence and death in the course of the five-year long civil war. Government forces have often employed heavy-handed tactics in efforts to oust rebels from the town. Last summer, Syrian government forces fired missiles at the town's center on market day at rush hour. At least 96 people were killed and another 200 injured.
Over the last week, there has been an uptick in fighting around Aleppo, Idlib, Latakia, and Damascus.
Mediators have struggled to get all factions in Syria's war to honor the February 27 cessation of hostilities deal, meaning peace talks in Geneva have repeatedly stalled. All sides are mired in distrust, and accuse one another of violating the truce. Representatives from one of the rebel groups walked out of talks earlier this week in protest of ongoing government airstrikes.
Some groups have managed to find common ground. Regional Kurdish security forces and pro-Syrian government forces declared a ceasefire in Qamashli, northeastern Syria, on Friday after a three-day outbreak of violence killed 26 people. A Reuters witness said that truce continued to hold on Saturday.
Islamic State militants also claim to have shot down a Syrian warplane flying over the countryside outside Damascus on Friday. Islamic State fighters released a message through their Amaq news agency, claiming that they had captured a pilot of a Syrian warplane whose aircraft crashed southeast of Damascus.
"The pilot, called Azzam Eid... was captured after he fell by parachute near the site where his plane crashed east of Damascus," Amaq Agency said in a statement.
Russian news agency Interfax said that the plane belonged to the Syrian Air Force. Citing a source in the Syrian military, Interfax added that the plane, a Mig-23, crashed because of a technical fault. On Friday, IS said that a Syrian warplane had been shot down, but did not specifically claim responsibility.
"The plane had recently undergone repairs," Interfax said. "There was no attack from the ground. It crashed because of a technical fault. The pilot ejected."
A video shared by Amaq purported to show the smoldering plane wreckage, part of which had a Syrian flag painted on it.
According to the SOHR, the plane crashed in the countryside outside of Damascus after flying over IS-controlled territory. The fate of the pilot is not clear.
On Friday, Staffan de Mistura, the UN special envoy for Syria, estimated that about 400,000 people had been killed over the last five years of civil war. Mistura urged key players in the war to help salvage the crumbling ceasefire agreement. Mistura added that the death toll was his own estimate, not an official UN statistic.
The envoy said he would continue to hold peace talks next week, regardless of "the worrisome trends on the ground."
Reuters contributed to this report