A U.N. photograph of chief U.N. chemical weapons investigator Ake Sellstrom handing over his report on an August 21 gas attack on Damascus suburbs shows that the report confirms use of the deadly nerve agent sarin.

"On the basis of the evidence obtained during the investigation of the Ghouta incident, the conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic ... against civilians, including children, on a relatively large scale," the report said.

"In particular the environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface to surface rockets containing the nerve agent sarin were used," it said.

The photo released by the United Nations shows Sellstrom giving the report, which will be officially released later on Monday, to U.N. Secretary-General Ban Ki-moon. By zooming in on the photo some of its contents can be clearly read.

The results of Sellstrom's investigation are not surprising. Several weeks ago U.S. Secretary of State John Kerry announced that sarin had been used in the chemical attack on the Ghouta region near Damascus.

It is not clear whether the report will include details that suggest culpability. Sellstrom's mandate is limited to investigating the facts, not assigning blame.

Some Western diplomats have said on condition of anonymity that information about the type of weapons and other details Sellstrom might possess could hint at government responsibility for the attack. Syria and Russia have blamed the August 21 attack on the rebels.

The rebels, the United States and other Western powers blame forces loyal to Syrian President Bashar al-Assad for the August 21 attack.