A Syrian airstrike slammed into a house in a rebellious suburb of Damascus early Monday, killing at least 13 people including eight children, activists said, as President Bashar al-Assad's regime ramped up its operations against the opposition strongholds ringing the capital.

Government forces have used warplanes and multiple rocket launchers over the past 24 hours in what activists described as some of the heaviest barrages of the Damascus region since the government launched an offensive in November to dislodge rebels from the capital's outskirts. At least 45 people were killed in a government barrage on Sunday, opposition groups said.

The air raid early Monday struck a home in the southern suburb of Maadamiyeh when residents were still inside, the Britain-based Syrian Observatory for Human rights and other activists said. Locals pulled 13 bodies — including those of eight children — from the rubble, the Observatory said, adding that at least seven more people remain trapped.

Syrian state media, however, refuted that account, and blamed rebels for the deaths in Maadamiyeh. The official SANA news agency said terrorists fired a shell at the neighbourhood from nearby Daraya, hitting a residential building and causing casualties.

'There are a lot of casualties'

"The noise from the bombardment is astounding today," a fighter who identified himself as Iyad said by satellite phone from an area near Maadamiyeh.

"The regime is using all kinds of weaponry, they are shelling Maadamiyeh from nearby mountains and we are hearing that there are a lot of casualties,' he said, adding that telephone lines to the area have been cut.

An amateur video posted online by activists showed young men walking over piles of rubble, searching for people as women, apparently trapped inside buildings, could be heard wailing and crying for help. A voice in the background said the video is of Maadamiyeh.

A man cried "God is great" as the camera closed in on what appeared to be a child's body covered in rubble. The child is face down on the ground next to another body, with a hand sticking out from under the rubble.

In another video, the bodies of at least two children could be seen, their faces bloodied from what appear to be wounds to the head. One of the two children, a toddler, was lying on a gurney partially covered in green blankets as a woman is heard crying and screaming : "Why? Why, oh God, why?"

The caption says the children were less than a year old and were killed in the Maadamiyeh attack Monday.

The videos appeared consistent with activist reports from the area.

Fresh airstrikes

Fighter jets also carried out fresh airstrikes on the suburb of Daraya, a strategic suburb close to a key military air base. Last week, the government said it has regained control over more than half of the suburb.

Iyad, the fighter outside Damascus, said the regime on Sunday dispatched reinforcements to Daraya. The fresh troops were trying to advance and hold the territory, but have been unsuccessful.

Monday's attacks come a day after airstrikes and heavy shelling killed at least 45 people in the Damascus area.

The deadliest attack was reported in eastern Ghouta district, where 24 people, including eight children, were killed by government air and artillery strikes. The rest of the casualties, including 13 rebels killed in clashes, were in other neighbourhoods outside the capital.

Regime warplanes also bombed targets in the north Monday, hitting rebel positions inside a sprawling air base in Idlib province in an effort to regain control of the facility.

Rebels captured the Taftanaz helicopter base, which includes an airstrip, on Friday, dealing a major blow to Assad's forces that have relied on its airpower in the fight against the opposition.

The Observatory said the rebels retained control of the Taftana base that had been used by the Syrian government to carry out airstrikes nationwide and transports troops and supplies around the country.

Shell lands near Turkish border

A shell fired from Syria landed on an empty field near the Turkish border village of Akcabaglar, in Kilis province late Sunday, damaging an olive tree, the state-run Anadolu Agency reported. No one was hurt.

NATO has begun deploying Patriot missiles along Turkey's southern border with Syria to protect the NATO ally country from any possible spillover from the civil war in Syria. The six Patriot anti-missile systems are scheduled to become operational later this month.

In recent months, Turkey fired artillery across the frontier to retaliate for Syrian shells hitting Turkish soil, after five civilians were injured in October.

It was not clear however, whether Turkish troops had retaliated to Sunday's shelling.

The fighting has rage in Syria at a relentless pace despite a recent diplomatic push to try to secure a peaceful settlement to the nearly 2-year-old conflict, which the U.N. estimates has killed more than 60,000 people.

In a speech earlier this month, Assad dismissed international calls to relinquish power and vowed to continue fighting rebels.

The speech was condemned by the U.S. and its Western and Gulf Arab allies, while Assad's backers in Russia and Iran said his proposal should be considered.

Those fighting to topple the regime, including rebels on the ground, have repeatedly said they will accept nothing less than the president's departure, dismissing any kind of settlement that leaves him in the picture.

Russia's Foreign Minister Sergey Lavrov criticized Western demands that Assad step down. While acknowledging that the initiatives to talk to the opposition, "probably don't go far enough," Lavrov called on the opposition to come up with their plan to end the bloodshed.

"If I were in the opposition's place, I would put forth my own ideas in response on how to establish a dialogue," Lavrov said Sunday during a visit to Ukraine.