The UN Syria envoy Staffan de Mistura voiced deep disappointment at the collapse of US-Russian talks to revive a Syria ceasefire, but vowed to keep working for a political solution.<br/><br/>The UN will continue to push energetically for a political solution of the Syrian conflict regardless of the very disappointing outcome of intense and long discussions among two crucial international stakeholders, the office of de Mistura said in a statement.<br/><br/>The statement came after the United States yesterday suspended negotiations with Russia on efforts to revive a failed ceasefire in Syria and set up a joint military cell to target jihadists. State Department spokesman John Kirby accused Russia and its Syrian ally of stepping up attacks on civilian areas.<br/><br/>Russia's foreign ministry meanwhile said it regretted the decision, blaming Washington for trying to shift responsibility for the failure onto Moscow. Russia and the United States have traded blame for the collapse last month of a short-lived ceasefire deal that would have marked the first step in a new effort to end the war that has killed 300,000 people since 2011.<br/><br/>De Mistura's office stressed though that the UN-backed humanitarian task force for Syria will continue its hard work in order to assist the unimpeded delivery of aid to vulnerable<br/>civilians in Syria.