UN experts will give “overwhelming” confirmation that chemical weapons were used in Syria, UN leader Ban Ki-moon predicted Friday, as he blasted President Bashar al-Assad as a war criminal.

Ban did not say that Assad’s forces carried out a suspected chemical arms attack near Damascus investigated by UN experts. But he said the Syrian leader has “committed many crimes against humanity.”

A UN team is expected to send its report on the August 21 attack to Ban on Monday. The UN leader stressed that he still does not have the report.

But he predicted: “I believe the report will be an overwhelming report that the chemical weapons were used.”