Syria's government and rebels have "chosen the path of war", a UN peacekeeping chief said as the world body ended its doomed monitoring mission to Damascus and deadlock persists among world powers over how to contain the spreading conflict.

Two weeks after former U.N. secretary-general Kofi Annan quit as mediator in frustration with the failure of a four-month-old truce, military observers have no peace on the ground to monitor and U.N. officials said on Thursday, Aug. 16 the last of the few dozen remaining team members would quit Damascus by August 24.

"It is clear that both sides have chosen the path of war, open conflict, and the space for political dialogue and cessation of hostilities and mediation is very, very reduced at this point," said deputy U.N. peacekeeping chief Edmond Mulet.

At a time when fighting is raging around Syria's biggest city, Aleppo, and tit-for-tat sectarian kidnappings have spread the Syrian conflict into fragile neighboring Lebanon, Western powers and Russia remain resolutely at odds in the Security Council over the fate of President Bashar al-Assad, according to Reuters.