The Pentagon is shown in Arlington, Virginia, U.S., September 11, 2017. REUTERS/Joshua Roberts

WASHINGTON (Reuters) - The U.S. military on Friday disclosed for the first time base-by-base data on sexual assault reports, showing a higher number of reports at big military installations like Naval Station Norfolk in Virginia as well as overseas hubs like South Korea.

Sexual assault in the military, which is defined as anything from groping to rape, is believed to be significantly higher than the number of reports. The Pentagon said it estimates that, in 2016, less than a third of service members who experienced a sexual assault reported it.

Still, that was an improvement in reporting from previous years, the Pentagon said.

According to the newly released data, a collection of U.S. bases in South Korea had a combined 211 reports of sexual assault while Norfolk had 270 reports of sexual assault in the 2016 fiscal year, which began in October 2015 and ended in September 2016. That is down slightly from 291 cases at Norfolk in 2015.

The Pentagon did not elaborate on the data but noted that the reports showed where a victim reported a sexual assault, not necessarily where the sexual assault occurred.

Sexual assault reports from other big bases in 2016 included: Fort Hood in Texas with 199 reports; Naval Base in San Diego, California, with 187 reports; Camp Lejeune in North Carolina with 169 reports; Camp Pendleton in California with 157 reports, and Fort Bragg in North Carolina with 146 reports.

The Pentagon announced earlier this year a record total of 6,172 sexual assault reports in 2016, compared with 6,082 the previous year. This was a sharp increase from 2012, when 3,604 cases were reported.

The U.S. military said it believes that a biannual anonymous survey provides a more accurate estimate of the number of sexual assaults. According to the latest survey, 14,900 service members experienced some kind of sexual assault in 2016, down from 20,300 in 2014.