Syrian activist groups say the government renewed air raids over the northern city of Aleppo on Tuesday, after Monday airstrikes left about 30 people dead.
Opposition groups said a mosque that was being used as a school is among the buildings hit by an explosive device described as a barrel bomb. They say the blast killed five people.
There was no immediate confirmation from the Syrian government. The state-run SANA news agency says a women and a child were killed in Aleppo, on Tuesday, after "terrorists" fired a mortar shell.
In recent days, forces loyal to President Bashar al-Assad have been slowly advancing into rebel-held areas of Aleppo which were seized by the opposition in 2012.
In another development, Russian officials said they expect the Syrian government to resume peace talks with the opposition next week, following an opening round of negotiations in Geneva that ended Friday with little progress.
The statements on Tuesday came as Russian Foreign Minister Sergei Lavrov hosted Syrian National Coalition President Ahmad Jarba for a meeting in Moscow.
Lavrov said Russia wants to keep regular contacts with the opposition, and is working with all sides to find a political solution to the Syrian crisis.
"We urge our European and American partners, the countries in the region to choose the same approach. We are convinced they should work with all sides in the Syrian conflict without exception - I mean of course political sides, and not terrorist groups," Lavrov said.
Jarba said the opposition also intends to continue the talks, and that Russia plays an important role in trying to reach a political solution.
Also Tuesday, Russian state media quoted Deputy Foreign Minister Gennady Gatilov as saying Syria plans to remove a large shipment of chemical weapons this month.
The shipments are part of a plan to rid Syria of chemical weapons by the middle of the year. U.S. officials last week criticized Syria for what they said was the slow pace at which the process is progressing.