The US military received 1,700 reported cases of sexual assault involving one or more of their personnel last year, the US Defence Department said.
Officials sought to play down what appeared to be a sharp rise in alleged assaults compared with 2003.
The increase reflected a greater willingness to report such attacks, a Pentagon spokesman said.
This year's statistics are also the first to include incidents in which civilians were involved.
Previous figures have only reflected cases in which both the alleged attacker and victim were military personnel.
In 2003, the number of sexual assaults reported was 1,012 and in 2002 it was 901.
"We are not alarmed about what appears on the surface to be a very substantial increase," Pentagon spokesman Lt Col Joe Richard said.
He said the military had taken a number of steps to encourage victims to report what has historically been an under-reported crime.
Last year, US Defence Secretary Donald Rumsfeld ordered a review of how the military handled such complaints, after a string of assaults on women soldiers and a rape scandal at the Air Force Academy.
Of the 1,700 cases reported in 2004:
- 880 involved an alleged assault by a military person against another
- 425 involved an alleged assault by a military person against a non-military person
- 99 involved an alleged assault by a non-military person against a military person
- 296 involved an unidentified assailant against a military person
Of those, 342 led to punitive action in the military justice system; 351 were deemed unsubstantiated or closed due to insufficient evidence; 51 were in civilian or foreign courts; and 278 closed because the assailant could not be identified.