At least 29 Syrian rebels including two field commanders were killed when a vehicle exploded in the central city of Homs on Sunday, a monitoring group said.
To the south, the capital Damascus saw heavy fighting as warplanes pounded an eastern suburb and a mortar strike hit the city's heavily defended centre, killing two people at the Damascus Opera House.
President Bashar al-Assad's forces are in firm control of the capital's centre, but rebels have been able to launch mortar and rocket attacks into downtown districts, sometimes hitting heavily secured upmarket areas and embassy grounds.
"Two citizens were martyred and eight others wounded ... by mortars fired by terrorists at the opera house," the state news agency SANA said, without specifying when the attack occurred or whether the theatre was in use at the time.
The explosion in Homs was at the al-Jaj market near a police base, the British-based Syrian Observatory for Human Rights said, adding that the death toll was expected to rise.
It was not immediately clear who carried out the blast.
The anti-Assad Observatory, which monitors violence on all sides through a network of sources in Syria, said at least five people including three children had also been killed in the Damascus suburb of Douma during shelling by government forces.
Government war planes bombarded the eastern suburb Mleiha during heavy fighting with rebels, the group said.
Elsewhere, government helicopters dropped barrel bombs in the northern province of Aleppo, in Deraa in the south and Latakia in the west, the group said.
Assad's forces also shelled an area around Kasab, a village in the north of Latakia province that rebels seized about two weeks ago.
While rebels confronted government forces across the country, rival anti-Assad groups fought one another in the easterly Hasaka province.
Late on Saturday, two fighters from al-Qa'ida's Syrian affiliate, the Nusra Front, were killed around the town of Markadah during fighting with an al-Qa'ida splinter group, the Islamic State of Iraq and the Levant, the Observatory said.