He said yesterday that access must include interviews and examination of witnesses, victims and medical personnel and the conduct of post-mortem examinations.
After months of negotiations, a 20-member UN team led by Swedish chemical weapons expert Ake Sellstrom arrived in Damascus on Sunday to investigate three sites where chemical weapons attacks allegedly occurred: the village of Khan al-Assal just west of the embattled northern city of Aleppo and two other locations being kept secret for security reasons.
Diplomats and chemical weapons experts have raised doubts about whether the experts will find anything since the alleged incidents took place months ago.
Ban said if the UN team reports that chemical weapons were used, it is up to the international community "to determine what course of action should be taken to prove this, first of all, (determine) accountability, and what needs to be done." The secretary-general reiterated that "if confirmed, the use of chemical weapons by any side under any circumstances must be held accountable and would constitute an international crime."
At the same time, Ban reiterated that "in order to credibly establish the facts, the mission must have full access to the sites of the alleged incidents ... To undertake the necessary analyses and to collect samples."
Syria is said to have one of the world's largest stockpiles of chemical weapons, including mustard gas and the nerve agent sarin, though it has never admitted possessing such weapons.