WASHINGTON — The U.S. military fired or disciplined nearly 500 workers for sexual harassment in a 12-month period, and nearly 13 percent of the complaints filed involved repeat offenders, according to new data.

The Pentagon on Thursday released its first formal report on sexual harassment amid months of criticism from Congress over how the department handles sexual assaults and related crimes.

According to the report, there were 1,366 reports of sexual harassment filed in the fiscal year that ended Sept. 30, involving 496 offenders across the services and National Guard. Officials acknowledged that much like sexual assault complaints, incidents of sexual harassment are vastly underreported, and they said there will be a concerted effort to increase reporting.

Sexual harassment involves unwelcome sexual advances, requests for sexual favors, and other verbal or physical conduct of a sexual nature that is tied to a person’s ongoing employment or interferes with the person’s work.

The report reveals that in the vast majority of the cases the victim was a young, lower-ranking woman and the offender a senior enlisted male service member, often in the same unit. The most frequent location of the harassment was a military base.

More than half of the complaints involved crude or offensive behavior, and another 40 percent were described as unwanted sexual attention.

Nearly 60 percent of the complaints were substantiated and the punishments ranged from court martial and firing to pay cuts, rank demotions, letters of reprimand, and other administrative actions.

The report also said that the military services are aware of the large number of repeat offenders and “are taking appropriate action.” Officials said they hope to use the data to begin to resolve any problems with department policy or programs.