KIMBERLY HEFLING, AP Education Writer

WASHINGTON (AP) — The number of sex offenses on college campuses reported to the Education Department has nearly doubled over a five-year period.

Department officials say in a letter to California Sen. Barbara Boxer that they believe the increase is the result of federal enforcement efforts and growing public attention to the issues of campus sexual assault.

There were nearly 3,360 sex offense cases reported to the department in annual crime statistics reports in 2009. But the letter released by Boxer’s office says there were more than 6,000 in 2013.

Education and law enforcement officials say sexual assault is an underreported crime, and the true number of such crimes is likely much higher.