UN observers wind up their mission in Syria on Sunday, after Damascus denied opposition claims that top regime official Vice-President Faruq al-Shara had defected as its armed forces pounded rebels in several key flashpoints across the country.

The United Nations won support from the West as well as Russia and China for its new envoy for Syria, veteran Algerian diplomat Lakhdar Brahimi who was named on Friday to replace Kofi Annan at the end of the month.

In Damascus, state television issued a statement from Shara's office after opposition and media reports that he had fled, saying: "Mr Shara has never thought about leaving the country or going anywhere".

Shara, 73, is the most powerful Sunni Muslim figure in the minority Alawite-led regime of President Bashar al-Assad and has served in top posts for almost 30 years.

Adding to the mystery, a former deputy oil minister who defected in March said Shara was actually under house arrest and that other top officials were being kept under surveillance.

"He has been trying to leave Syria," Abdo Hussameddin told Al-Arabiya television. "But there are a series of circumstances that prevent him from leaving, especially the fact that he has been under house arrest for some time."

Assad's regime has already been hard hit by a series of defections since the anti-regime revolt erupted in March 2011, including former prime minister Riad Hijab and high profile general Manaf Tlass -- a childhood friend of Assad.

"Initial reports show that there was an attempted defection, but that it failed," the rebel Free Syrian Army (FSA) said.

The conflicting reports came as UN chief observer General Babacar Gaye accused both sides in the 17-month conflict of failing to protect civilians who have borne the brunt of the increasingly brutal violence.

'Obligations to civilians have not been respected'

"Both parties have obligations under international humanitarian law to make sure that civilians are protected," Gaye told reporters in Damascus ahead of the mission's end at midnight on Sunday.

"These obligations have not been respected."

The UN Security Council had ordered the withdrawal of UN observers in Syria on Thursday.

The UN originally sent 300 unarmed military observers to Syria in April but its patrols were suspended in June because of the mounting violence and the force was cut back.

The Security Council last month insisted that the UN Supervision Mission in Syria (UNSMIS) could only go on if the violence eased.

On the ground, as Muslims the world over marked Eid, the celebrations at the end of the holy month of Ramadan, Syrians faced another daily cycle of bloodshed.

The military launched new air strikes on Aazaz in the northern province of Aleppo, three days after about 40 people were killed in the rebel-held town, according to the Syrian Observatory for Human Rights.

It also pounded areas of Aleppo, the northern commercial hub near the Turkish border.

In Damascus, fighting broke out in the heavily populated southern district of Tadamun, showing the rebels are still resisting despite government forces last month claiming they had retaken the capital.

Rebels also targeted a military convoy besieging the neighbouring Al-Hajar Al-Aswad district near the country's biggest Palestinian refugee camp, killing at least four soldiers and one rebel, the Observatory said.

It reported at least 99 deaths Saturday, including 12 rebels and five civilians killed in army shelling and fighting in Herak in the southern province of Daraa, cradle of the uprising.

And in a gruesome sign of the escalating brutality, the Observatory said dozens of bodies had been found dumped in several areas of Damascus province.

Overall the death toll has surged to at least 23,000 people, while the UN puts the toll at 17,000.

The intensified fighting has sent thousands more Syrians fleeing into neighbouring countries, particularly Turkey. The UN says that at least 170,000 have fled and another 2.5 million inside Syria need aid.