Syrians woke up to air strikes near Damascus on New Year's Day and the closure of Aleppo airport after repeated rebel attacks, casting doubts on efforts to end the 21-month conflict.

The brutality of the war was highlighted in a graphic new video posted on the Internet by the Syrian Observatory for Human Rights, allegedly showing soldiers stabbing two prisoners to death.

And in a fresh blow to President Bashar al-Assad, a Turkish diplomat said some 20 Syrian soldiers, including a general, defected on Tuesday and fled to Turkey, rear-base of the insurgents battling the regime.

"The soldiers who fled to Turkey include a general, three colonels and several other officers," the diplomat told AFP in Ankara. Dozens of senior officers, as well as diplomats and political figures, have defected since the conflict began.

At least 69 people were killed across Syria, said the Observatory, which has put at more than 46,000 the overall death toll since the conflict erupted in May 2011.

Warplanes bombed the northeastern and southwestern suburbs of Damascus in a fresh bid to push rebels further from the capital, and troops attacked insurgent strongholds on the road to Damascus airport, the Observatory said.

At least 13 people were killed in the capital, the watchdog said.

Battles have raged for weeks outside Damascus where insurgents have set up rear bases.

In northern Syria, where insurgents hold huge swathes of territory, authorities announced the closure of Aleppo airport after rebel attacks.

An airport official told AFP the facility would be closed "for a very short period of time" as the army tries to regain control of rebel-held areas around it and to avoid a "humanitarian disaster."

"There have been continued attempts by opposition militants to target civilian aircraft, which could cause a humanitarian disaster," the official said.

Analysts say the army is also set on taking total control of Damascus and its immediate surroundings to create conditions necessary for future dialogue after the regime said it welcomed any initiative for talks to end it.

Prime Minister Wael al-Halaqi told parliament on Monday that the government would "respond to any regional or international initiative that would solve the current crisis through dialogue and peaceful means."

His comments came after UN and Arab League envoy Lakhdar Brahimi said on Sunday that he had crafted a ceasefire plan "that could be adopted by the international community."

The proposal involved a ceasefire, the formation of a government and an election plan, and was based on an agreement world powers reached in Geneva in June.

The opposition has already rejected the Geneva accord and insist that Assad must go before any dialogue can take place.

Dozens of the president's opponents took to the streets of the central Damascus district of Salhiyeh on New Year's Eve calling for the fall of the regime and wishing Assad "a black year."

"May God protect the (rebel) Free Syrian Army" and "Victory to the revolutionaries!" they also chanted.

Violence ravaged Syria into 2013 also with a gruesome video posted online by the Observatory.

"We cannot say where and when this happened but this video shows how savage the Syrian conflict has become," Observatory chief Rami Abdel Rahman told AFP.

The clip shows men in military fatigues, identified as regular army soldiers by the Observatory, slashing to death two prisoners with knives.

"They are Arur's men," one of the killers says, referring to a Syrian Salafist imam based in Saudi Arabia who has called on rebels to murder members of Assad's Alawite community.

The video shows an assailant stabbing one of the prisoners in the back and the ribs and another man trampling the prisoners, battering them with cement blocs and then covering them in rubble and leaving them to die.

AFP could not confirm the footage.

The video appeared a day after activists reported finding dozens of mutilated bodies, another sign of the gruesome nature of the conflict.

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