Syrian warplanes bombed rebel targets with renewed intensity on Tuesday after the end of a widely ignored four-day truce between President Bashar al-Assad's forces and insurgents.
State television said "terrorists" had assassinated an air force general, Abdullah Mahmoud al-Khalidi, in a Damascus suburb, the latest of several rebel attacks on senior officials.
In July, a bomb killed four of Assad's aides, including his brother-in-law Assef Shawkat and the defence minister.
Air strikes hit eastern suburbs of Damascus, outlying areas in the central city of Homs, and the northern rebel-held town of Maarat al-Numan on the Damascus-Aleppo highway, activists said.
Rebels have been attacking army bases in al-Hamdaniya and Wadi al-Deif, on the outskirts of Maarat al-Numan.
Some activists said 28 civilians had been killed in Maarat al-Numan and released video footage of men retrieving a toddler's body from a flattened building. The men cursed Assad as they dragged the dead girl, wearing a colourful overall, from the debris. The footage could not be independently verified.
The military has shelled and bombed Maarat al-Numan, 300 km (190 miles) north of Damascus, since rebels took it last month.
"The rebels have evacuated their positions inside Maarat al-Numaan since the air raids began. They are mostly on the frontline south of the town," activist Mohammed Kanaan said.
Maarat al-Numan and other Sunni towns in northwestern Idlib province are mostly hostile to Assad's ruling system, dominated by his minority Alawite sect, an offshoot of Shi'ite Islam.
Two rebels were killed and 10 wounded in an air strike on al-Mubarkiyeh, 6 km (4 miles) south of Homs, where rebels have besieged a compound guarding a tank maintenance facility.
Opposition sources said the facility had been used to shell Sunni villages near the Lebanese border.
'We'll fix it'
The army also fired mortar bombs into the Damascus district of Hammouria, killing at least eight people, activists said.
One video showed a young girl in Hammouria with a large shrapnel wound in her forehead sitting dazed while a doctor said: "Don't worry dear, we'll fix it for you."
Syria's military, stretched thin by the struggle to keep control, has increasingly used air power against opposition areas, including those in the main cities of Damascus and Aleppo. Insurgents lack effective anti-aircraft weapons.
But it is unclear how he can find any compromise acceptable to Assad, who seems determined to keep power whatever the cost, and mostly Sunni Muslim rebels equally intent on toppling him.
Big powers and Middle Eastern countries are divided over how to end the 19-month-old conflict which has cost an estimated 32,000 dead, making it one of the bloodiest of Arab revolts that have ousted entrenched leaders in Tunisia, Egypt and Libya.
The United Nations said it had sent a convoy of 18 trucks with food and other aid to Homs during the "ceasefire", but had been unable to unload supplies in the Old City due to fighting.
"We were trying to take advantage of positive signs we saw at the end of last week. The truce lasted more or less four hours so there was not much opportunity for us after all," said Jens Laerke, a U.N. spokesman in Geneva.
The prime minister of the Gulf state of Qatar told al-Jazeera television late on Monday that Syria's conflict was not a civil war but "a war of annihilation licensed firstly by the Syrian government and secondly by the international community".
Sheikh Hamad bin Jassim al-Thani said some of those responsible were on the U.N. Security Council, alluding to Russia and China which have vetoed three Western-backed U.N. draft resolutions condemning Assad.
He said that the West was also not doing enough to stop the violence and that the United States would be in "paralysis" for two or three weeks during its presidential election.