More than 140 people were killed in government and Russian air strikes across Syria within 24 hours, according to sources and monitors.
At least 80 people were killed in Aleppo city and nearby towns by a series of Russian and regime air strikes on Friday, sources told Al Jazeera.
About 25 areas within Aleppo province were hit by the air strikes.
The deadly raids came after at least 61 people were killed and more than 100 others wounded after Syrian government air strikes hit a marketplace in a Damascus suburb, sources said.
An officer of the Syria Civil Defense in the Damascus suburbs branch told Al Jazeera that the air raids struck a busy market in Douma on Friday, killing at least 61 and injuring more than 100 others.
Douma, east of Damascus, has been under intense government attack for weeks now.
Witnesses said missiles were fired into the marketplace in a rebel-held part of Douma.
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"This is the second time this market has been targeted in Douma," the civil defence officer said over phone from Douma.
"There are only civilians here - no army and no opposition forces. Residents do not permit any armed person in this area.
"This market is at the heart of Douma and supplies everyone here. Lots of farmers come here every morning to sell their items. The market was intentionally targeted."
A local activist, speaking to Al Jazeera on the condition of anonymity, said Douma was under heavy attack since Friday morning.
"Every 10 minutes we are under attack - rocket attacks and air strikes. They bombed a local market ... we expect a rising death toll," he said.
"Every corner of Douma is being bombed."
The attack came as the US, Russia, Saudi Arabia, Turkey and Iran met in Vienna with the aim of achieving a political settlement to help end the war in Syria.
Friday's talks in the Austrian capital included an Iranian delegation for the first time.
Meanwhile, Syria's main political opposition group, the Syrian National Council, issued a statement on Friday accusing Russia of committing war crimes in Syria, one month after Russia started its air campaign in support of the Syrian regime.
"The Russian invaders have committed war crimes since they launched the aggression on Syria a month ago, bombing residential areas, hospitals, schools and bakeries," the statement said.
"Nearly 1,716 civilians, including women and children, were killed, while 12 hospitals in three provinces, as well as bakeries in Ter Maaleh and Saraqib, were hit by the Russian air strikes."
Additional reporting by Diana Al Rifai. Follow her on Twitter @D_R_23
Source: Al Jazeera