Family members are often forced to watch, according to the report, and gang rape is not uncommon. In addition, it says, there is an “alarming lack” of medical and psychological support for survivors of the attacks.

This sexual violence was “consistently identified by Syrian women, men and community leaders as a primary reason their families fled the country,” according to the report, which is based on interviews in November with refugees, officials, aid workers and others in Jordan, Turkey, Lebanon and Iraq.

The number of Syrian refugees living in neighboring countries has grown to more than 600,000. Many live in camps, while others pack into rented apartments or squat in schools, public buildings or sheds — unsafe environments that the report says can lead to sexual assaults, elevated levels of domestic violence and early or forced marriages.