Sexual assaults at American military academies increased sharply in the last academic year, says a new report from the department of defence.

Incidents of sexual assault rose by 60 percent during 2010-2011. A total of 65 reports involved cadets compared to a total of 41 reports in the previous year, CNN reported.

The defence department was, however, unable to cite definitive causes for the increase. As part of the study, site visits were conducted at the US Military Academy in New York, US Naval Academy in Annapolis and the US Air Force Academy in Colorado.

Policies, training and procedures at the academies were reviewed, and focus groups were held with cadets.

"We know that the military academies are similar to college campuses around the country in that sexual harassment and assault are challenges that all faculty, staff and students need to work to prevent," said Maj. Gen. Mary Kay Hertog, director of the Sexual Assault Prevention and Response Office.

"However, when it does occur, we owe it to those who have been victimised, and to every cadet, to do everything possible to provide needed support and to hold those who commit sexual assault appropriately accountable," she said.