President Bashar al-Assad made a rare public appearance for the Muslim holiday of Eid on Sunday as activists staged protests across Syria to rage against the regime.
The new UN peace envoy to Syria, Lakhdar Brahimi, said it was no longer a question of "preventing civil war" in Syria but rather stopping it.
Assad joined prayers at a Damascus mosque for the Eid al-Fitr festival, his first appearance in a public place since a bomb blast last month killed four top security officials, although he has been seen on television since then.
But despite the religious holiday, his forces were still in deadly action on the ground, shelling several rebel hubs and clashing with opposition fighters in Damascus itself, a monitoring group said.
Six children, one as young as five and including four from the same extended family, were killed by shelling near their home in the rebel-held town of Maaret al-Numan in the northwestern province of Idlib, said the Syrian Observatory for Human Rights.
In all, at least 56 people -- including 22 civilians -- were killed on the first day of Eid, the festival celebrated by Muslims to mark the end of the holy month of Ramadan, the Britain-based group said.
UN observers were winding up their troubled mission on Sunday in the face of the escalating violence and a failure by world powers to agree on how to tackle Assad and bring about peace to the strategically vital Middle East state.
Syrians joined prayers and staged demonstrations for Eid, taking place for the second year under the shadow of a conflict the Observatory says has now claimed 23,000 lives while the UN gives a death toll of 17,000.
"Eid is here, Eid is here, God curse you, O Bashar," protesters in Qudsaya in Damascus province sang to the tune of Jingle Bells, according to amateur video posted on YouTube.
"There is no Eid for Bashar, nothing is holy for him. They are willing to strike anywhere, mosques, hospitals, bakeries, children. What kind of Eid is this?" Abu Issa, a 39-year-old builder in Aleppo, asked an AFP correspondent.
Several families said they would not make the traditional visit to cemeteries to place flowers on the tombs of departed loved ones because of security fears.
"The children in the Old City district are sad because there are no sweets, no food, no gifts, no new clothes this Eid," added a young man from the central city of Homs who gave his name as Abu Bilal.
While demonstrators called for the fall of the regime, Assad himself joined top government and ruling Baath party officials at Eid prayers in Al-Hamad mosque.
"Syria will triumph against the Western-American plot being supported by the Wahhabis and takfiris," or Sunni Muslim hardliners, said imam Sheikh Mohammed Kheir Ghantus, echoing the regime's long-standing rhetoric.
Assad, from the minority Alawite community of an offshoot of Shia Islam, has characterised the conflict as a battle against a foreign "terrorist" plot aided by the West and its allies in the region, led by Sunni powerhouse Saudi Arabia.
-- German and British spies --
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Press reports said on Sunday that British and German spies were involved in covert operations to help Syrian rebels.
"We can be proud of the significant contribution we are making to the fall of the Assad regime," an official from Germany's BND foreign intelligence service told the weekly Bild am Sonntag.
The paper said German spies were stationed on a boat off the Syrian coast and also active at a NATO base in Turkey, a one-time Syrian ally whose government is now staunchly opposed to Assad and is sheltering Free Syrian Army (FSA) rebels.
Britain's Sunday Times said British intelligence was helping rebels launch successful attacks on government forces with information gathered from their listening posts in nearby Cyprus.
It said the most valuable intelligence had been about the movements of troops towards Aleppo, the scene of fierce fighting.
Jordan meanwhile said four rockets fired from neighbouring Syria fell inside its northern border area, wounding a four-year-old girl and sparking a letter of protest.
"We are in touch with the Syrian sides to determine what happened," Information Minister and government spokesman Samih Maaytah told AFP.
"The Jordanian government summoned the Syrian ambassador in Amman and gave him a letter of protest. Jordan rejects what happened and will make sure it does not occur in the future," Maaytah said.
Zayed Hammad, head of the prominent Jordanian Ketab and Sunnah charity which cares for more than 50,000 Syrian refugees near the border, said the rockets fell on Torrah border village, "injuring several people".
Jordan currently hosts more than 150,000 Syrian refugees. Many of them come under Syrian army fire as they flee to the kingdom, whose troops provide covering fire.
The UN observer mission ended at midnight on Sunday, just days after new international envoy Brahimi was named to replace Kofi Annan.
Brahimi, a veteran Algerian diplomat, has won support from the West as well as China and Russia, and even Syria itself, although the White House said it would be seeking clarifications on the terms of his mandate.
"A civil war, it is the cruellest kind of conflict, when a neighbour kills his neighbour and sometimes his brother, it is the worst of conflicts," Brahimi said in an interview with France 24 television in Paris.
"There are a lot of people who say that we must avoid civil war in Syria, me I believe that we are already there for some time now. What's necessary is to stop the civil war and that is not going to be easy."
Turkish authorities on Sunday crossed the Syrian border to distribute food and other supplies to hundreds of Syrians who have been forced from their homes and are massed at the border, emergency officials in the region said.
What began in March 2011 as a peaceful uprising has descended into an armed revolt with fighting reaching the two main cities of Damascus and Aleppo and atrocities reported on both sides, but particularly by the regime.
The West is demanding that Assad step down as part of any political deal but is opposed by Syria's traditional allies in Moscow and Beijing which see it as foreign-imposed regime change.