Secretary-General Ban Ki-moon says he believes there will be "an overwhelming report" from U.N. inspectors that chemical weapons were used in an attack in Syria on Aug. 21.
The U.N. chief also said that President Bashar Assad's regime "has committed many crimes against humanity."
Ban made the comments Friday shortly before the chief chemical weapons inspector, Ake Sellstrom, said the report was finished.
The secretary-general thought his speech and response to questions from a women's group were not being broadcast, but they were shown on U.N. television.
Speaking by telephone from the Netherlands, Sellstrom told The Associated Press on Friday that he didn't know exactly when the report would be released publicly but that he would deliver it to Ban in New York this weekend.
Sellstrom confirmed that "it's done, but when to present it is up to the secretary-general."
He declined to comment on the report's conclusions.
Sellstrom's inspection team was charged with determining whether deadly agents were used in Syria, not who was responsible.