The tiny corpses, faces pale and grimy, lay side by side, wrapped in a red blanket.

They are the latest child casualties in the bloody Syrian civil war. They are also grisly evidence of the carnage in the besieged Syrian city of Daraya over the weekend.

Published Monday by the opposition outlet Shaam News Network, the image underscores the horrors in Daraya. At least 245 people were found dead in the Damascus suburb over the weekend, opposition activists say.

Mass killings have been reported regularly across Syria during the nearly 18-month-long crisis. Like the others, this incident sparked international outrage.

The killings in Daraya need to be investigated "immediately and impartially," said U.N. spokesman Martin Nesirky, passing along remarks from U.N. Secretary-General Ban Ki-moon.

"Whoever is responsible needs to be held accountable," Nesirky said.

"Daraya is being targeted because it is the closest to the capital, and it is one of the first cities that revolted against the Assad regime and was the spearhead of the peaceful demonstrations in the beginning of the revolution," said Rafif Jouejati, a spokeswoman for the opposition Local Coordination Committees of Syria.

Opponents of the Syrian regime posted video of mass burials Sunday, a day after the remains were found in Daraya.

In one of the videos, one woman shouted " 'God is greater' as soldiers raided her house," an opposition member who goes by the name Abu Kanan said from the city. "The soldiers arrested her with five men from her family and executed them."

The remains of the dead were gathered in a mosque to be identified, and rebel fighters posted video of dozens of bloodied corpses online.

The "army started picking up young men from the streets, from their homes, and conducted summary executions" before government troops pulled back to the city's outskirts Sunday night, he said.

State-run and pro-government TV networks aired glowing descriptions of Daraya's recapture by forces loyal to Syrian President Bashar al-Assad after a weeklong siege. It blamed the deaths on "terrorists" driven out by the army.

Opposition activists said the dead were victims of a rampage by government troops after the rebel Free Syrian Army withdrew from the city late Friday.

The LCC said the 39 corpses of people kidnapped and slaughtered were handed over to to families Monday.

Syrian television aired a different account, showing residents who thanked government troops for coming to their rescue amid bodies still sprawled in the streets.

"Thanks to the military who is protecting us," one man told the pro-government network Al-Dounia. "Thank you for coming."

"Every time we get into a region where the terrorists were present, we discover what these terrorists know best -- killings, massacres and all in the name of freedom," the report said.

The development has prompted international revulsion. The French Foreign Ministry said Monday it is "deeply shocked by the discovery of mass graves" in "what appears to be a massacre of civilians."

Daraya was the scene of some of the first peaceful protests that were attacked by security forces in al-Assad's clampdown on opposition that began in March 2011 and became a civil war.

CNN cannot independently verify reports of death tolls, as the Syrian regime has severely limited access by international journalists.

In other developments:

Chemical weapons use would justify intervention, France says

France warned the Syrian regime that using chemical weapons could be grounds for intervention.

"We remain vigilant with our allies to prevent the use of chemical weapons by the regime which for the international community would be a legitimate reason for direct intervention," President Francois Hollande said Monday in a speech to French ambassadors.

Britain and the United States have said they would "revisit" their approach to Syria if the Syrian government uses chemical weapons, the British prime minister's office said last week.