GENEVA — U.N. rights investigators have concluded that Syria’s air force carried out a deadly nerve gas attack in April that drew international condemnation, while Russian strikes helped to destroy hospitals that could have treated victims.

In addition to the sarin gas attack — which killed more than 80 people in a rebel-held town on April 4 — Syrian government forces repeatedly used chlorine gas between March and July, the U.N. Commission of Inquiry on Syria reported.

The findings, presented in Geneva, go further than those from the Organisation for the Prohibition of Chemical Weapons. That group confirmed in June that sarin was used in Khan Sheikhoun, but did not identify the attacker.

The Commission of Inquiry said that it collected evidence from dozens of victims, witnesses and emergency workers, as well as from satellite images.