UN Secretary-General Ban Ki-moon has pleaded for a diplomatic solution to the Syrian conflict, even as world powers appeared to be moving toward military strikes against president Bashar Assad's regime.

Mr Ban said the UN team investigating the alleged chemical attack must be given time to establish the facts. They are due to visit an eastern suburb of the capital, Damascus, affected by the strike killed hundreds of people.

Mr Ban said the team already has already "gathered valuable samples and interviewed victims and witnesses."

He also urged the United Nations Security Council, whose permanent members are bitterly divided over Syria, not to go "missing in action" as the Syria crisis deepens.

Mr Ban was speaking in the Great Hall of Justice at the Peace Palace in The Hague, which is marking its 100th anniversary. The timing of the celebrations was uncomfortable; the Peace Palace opened its doors in 1913 as a venue for peaceful resolution of conflicts and currently houses the United Nations' International Court of Justice but Washington is building support for a military attack on Syria - possibly without UN backing.

Without explicitly referring to moves apparently preparing for military action by Washington and its allies, Mr Ban urged a peaceful resolution to Syria's civil war.

"Here in the Peace Palace, let us say: Give peace a chance. Give diplomacy a chance. Stop fighting and start talking," he said.