International peace envoy Kofi Annan warned Saturday of an all-out sectarian war in Syria, holding President Bashar al-Assad as the first responsible to act to end the conflict.
"The spectre of an all-out war with a worrying sectarian dimension grows by the day," he told a ministerial meeting on Syria in Doha.
"The situation is complex and it takes everyone involved in the conflict to act responsibly if the violence is to stop. But the first responsibility lies in the Syrian government and President Assad," he said.
He said he expressed to Assad during his visit to Damascus earlier this week his "deep concerns" and that the crisis is "at a tipping point."
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Up to 300 unarmed UN observers have deployed in Syria since a putative ceasefire brokered by Annan went into effect in April as part of his six-point peace plan, which also stipulated that the army must pull out of towns and cities.
"I told Assad he must act now to implement all points of the plan, and must make bold and visible steps immediately to radically change his military posture and honour commitment to withdraw heavy weapons and cease all violence," Annan said.
He also said he told Assad to release detainees, open up the country to international humanitarian aid and allow people to express their opinion freely as "this is essential to demonstrate his seriousness to the Syrian people and the international community."
Monitors say more than 13,400 people have been killed across Syria since an anti-regime uprising erupted in March 2011, including nearly 2,300 since the ceasefire technically went into effect on April 12.
Most of Syria's 22-million population are Sunni Muslims, while other minorities include 10 percent Christians and 12 percent Alawites -- an off-shoot Shiite community to which Assad belongs.