Airstrikes by Syrian jets and shells from tanks leveled a neighbourhood in a restive city near Damascus, the capital, reportedly killing 18 people, including four women and five children.
Tuesday's bombardment of the city of Douma, northeast of the capital, left residents scampering over a huge expanse of rubble and using their hands to dig up mangled bodies, according to activist videos posted online.
The army also fired mortar bombs into the Damascus suburb of Hammouria, killing at least eight people, activists said.
In Damascus city, Syrian fighter jets reportedly hit targets inside the capital for the first time on Tuesday, dropping four bombs on the neighbourhood of Jobar, near the opposition-held suburb of Zamalka, where rebel fighters were locked in fierce clashes with the army.
There were no reports of casualties in the bombing run, which AFP news agency correspondents said was heard across the capital.
Also on Tuesday, Syrian rebels claimed in an Internet statement they had assassinated an air force general in Damascus.
State television said that Major General Abdullah Mahmud al-Khalidi, was killed in the northern Damascus district of Rukn al-Din by "terroritsts".
The general, who it said was in charge of training, as well as an air force intelligence specialist, was shot dead on Monday evening as he left a friend's home, a security source in Damascus told AFP on condition of anonymity.
'Heaviest bombing campaign'
In the northwestern province of Idlib, activists said 28 civilians had been killed in the town of Maarat al-Numan and released video footage of men retrieving a toddler's body from a flattened building.
The army has been battling rebels for weeks for control of the town, which is on a key supply route between Damascus and the northern city of Aleppo.
The latest violence came a day after what activists called the heaviest and most widespread bombing campaign nationwide.
Syria's rebels tell Al Jazeera why foreign fighters are joining their ranks
The death toll for what was supposed to be a four-day cease-fire between government forces and rebels exceeded 500. The truce, brokered by UN-Arab League envoy Lakhdar brahimi, ended on Monday, and each side accused the other of violating it.
Activists speculated that the government's heavy reliance on air power reflected its inability to roll back rebel gains, especially in the north of the country near the border with Turkey, where rebels have control of swathes of territory.
Tuesday also saw clashes between rebels and troops backed by Palestinian fighters at the Yarmuk refugee camp, home to 148,500 Palestinians on the edge of the capital.
Anwar Raja, spokesman for the pro-Damascus Popular Front for the Liberation of Palestine-General Command, said its forces clashed for about an hour with rebels trying to infiltrate the camp but that there were no casualties.
There are more than 510,000 Palestinian refugees living in Syria, and their leadership is largely supportive of President Bashar al-Assad's regime.
'Extermination of Syrians'
With Brahimi due in China in a bid to revive struggling peace efforts, Sheikh Hamad bin Jassem al-Thani, the Qatari prime minister, said the international community's failure to halt the fighting was making it complicit in the violence.
"What is happening in Syria is not a civil war but a war of extermination against the Syrian people," he told Al-Jazeera.
The war, he said, was being waged "with a license to kill, endorsed firstly by the Syrian government and secondly by the international community."
Meanwhile, Ahmet Davutoglu, the Turkish foreign minister, said at a news conference: "There is no point in engaging in dialogue with a regime that continues to carry out such a massacre against its own people, even during [the Muslim festival of] Eid al-Adha."
Reacting to Davutoglu, the Syrian foreign ministry, issued a statement, saying that Ankara "refuses to review its policy of destructive criticism which proved its failure on the ground and continues to publicly target the security and stability of neighbouring Syria".
In-depth coverage of escalating violence across Syria
Davutoglu's comments came a day after after Moscow called for negotiations with Damascus as the only way to end the escalating conflict.
Sergei Lavrov, the Russian foreign minister called on the West and regional players including Turkey to start negotiating with President Bashar al-Assad as well as the opposition to pave the way for a political solution in Syria, wracked by almost 20 months of conflict.
"Hardly anything will be accomplished without dialogue with the government, and that is the only problem that remains in the path towards a political process," Lavrov said after a meeting Brahimi.
Ankara had backed Brahimi's call for a Davutoglu said the failed truce left Turkey "deeply upset."
Brahimi said on Monday that the UN "is not considering" sending an armed peacekeeping force to Syria, though relevant officials were conducting contingency planning in case the Security Council ordered such a mission.
That is highly unlikely with Russia and China wielding vetoes.