UNITED NATIONS - A report by UN chemical weapons experts is expected to confirm that poison gas was used in an August 21 attack on Damascus suburbs that killed hundreds of people, U.N. Secretary-General Ban Ki-moon said on Friday.

“I believe that the report will be an overwhelming, overwhelming report that chemical weapons (were) used, even though I cannot publicly say at this time before I receive this report,” Ban said at a U.N. meeting. He was obviously referring to an eagerly awaited report by the U.N. expert team led by Ake Sellstrom of Sweden.

UN spokesman Farhan Haq, who faced a string of questions on the secretary-general’s statement,  said that Ban does not have Sellstrom’s report yet. Ban has said previously, however, that he was in contact with Sellstrom and had urged him to expedite his conclusions.

Ban also said on Friday that Syrian President Bashar al-Assad “has committed many crimes against humanity,” though he did not say whether it was Assad’s forces or rebels who used the chemical weapons in the August 21 attack.

While Sellstrom’s report will not explicitly pin the blame on either side, diplomats say the facts they gathered could suggest which side in the 2-1/2 year civil war was responsible.

The United States and other Western powers blame forces loyal to Assad for the attack. Russian President Vladimir Putin asserts there is “every reason to believe” it was carried out by rebels.