Syrian fighter jets have blasted the rebel-held town of Maaret al-Numan, killing at least 44 people, including 23 children, rescue workers said.
Among those who died on Thursday died was a nine-month-old baby.
Rescuers said bombs destroyed two residential buildings and a mosque, where many women and children were taking refuge, in the strategic northwestern town, which was captured by rebels on October 9 in a push to create a buffer zone along the Turkish border.
"We have recovered 44 corpses from under the rubble," one worker told an AFP news agency correspondent at the scene.
In a makeshift field hospital, the correspondent saw at least 32 bodies wrapped in white sheets, including six children and many mutilated corpses, as well as plastic bags marked "body parts".
The correspondent said one child was decapitated while the body of a second, still on his bicycle, was pulled from the rubble.
"At the moment it seems only three people survived the attack, including a two-year-old child," said medic Jaffar Sharhoub.
"He survived in the arms of his dead father."
A resident who spoke to AFP on condition of anonymity said several of those killed had just returned to their homes.
"They thought the danger had passed."
Several fighter jets flew over Maaret al-Numan and the surrounding area throughout Thursday morning.
They made short dives to drop at least 10 bombs on the town and its eastern outskirts, near the besieged Wadi Deif army base which came under heavy bombardment by the rebels.
In early evening, the rebels launched what they said was a "final assault" on the base, which is a key depot for tanks and fuel supplies.
Hundreds of fighters attacked the base, a frontline AFP correspondent reported. Three tanks were destroyed and at least six soldiers surrendered, rebel officers said.
The base is situated two kilometres from the Damascus-Aleppo highway, of which the rebels control a stretch of several kilometres. That is severely impairing the army's ability to resupply units under fire in the northern metropolis for the past three months.
In-depth coverage of escalating violence across Syria
In the capital, a suicide bomber on a motorcycle blew himself up just 300 metres from the interior ministry without causing any casualties, a security source said.
The bombing came on the eve of arrival of Lakhdar Brahimi, the UN-Arab League envoy, in Damascus to press his call for a ceasefire during the four-day Eid al-Adha Muslim holiday starting on October 26.
Speaking in neighbouring Jordan, Brahimi said he hoped that such a temporary ceasefire could form the basis for a longer lasting truce, warning that the alternative would be disastrous for the whole region.
"If the ceasefire is implemented, we can build on it and make it a real truce as well as the start of a political process that would help the Syrians solve their problems and rebuild their country," Brahimi said in Amman.
"If the Syrian crisis continues, it will not remain inside Syria. It will affect the entire region," he added.
Scepticism over truce
The Algerian diplomat's visit to Syria for talks with Foreign Minister Walid Muallem on Saturday will be his last stop on a tour of countries that play influential roles in the crisis - Egypt, Turkey, Saudi Arabia, Iran, Iraq, Lebanon and Jordan.
The envoy will also meet with President Bashar al-Assad "very, very soon, but not on Saturday," Brahimi's spokesman, Ahmad Fawzi, told AFP.
Asked whether any optimism was warranted over the Damascus talks, foreign ministry spokesman Jihad Maqdisi said: "Let's see what Brahimi has to say."
Serious doubts have been raised about Brahimi's plan to halt the bloodshed, even temporarily.
"I don't know whether they will all agree at the higher level or not on the ceasefire proposal, but on the ground you have pro- and anti-regime forces that do not respond to any authority," said Rami Abdel Rahman of the UK-based Syrian Observatory for Human Rights.
Damascus said it is ready to discuss with Brahimi his proposal but wanted assurances that countries with influence on the rebels would pressure them to reciprocate.
The exiled opposition said it would welcome any ceasefire but insisted the ball is in the government's court to halt its daily bombardments.