DENVER -- Three U.S. senators have asked the Pentagon inspector general to independently investigate charges that the Air Force Academy has not properly responded to reports of sexual assaults against female cadets.

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The number of female Air Force Academy cadets reporting sexual assault continues to grow in the wake of a 7NEWS investigation.

Sen. Wayne Allard told 7NEWS that 18 women have come forward and claimed that they were raped and then punished while they were cadets at the prestigious military academy.

Allard requested a Pentagon investigation after 7NEWS Investigates showed female cadets who were ostracized, punished and sometimes drummed out of the academy after reporting sexual assaults.

Sen. Susan Collins, R-Maine, chairman of the Senate Governmental Affairs Committee, and Sen. Joe Lieberman, D-Conn., the top Democrat on the committee, said in a letter to Defense Department Inspector General Joseph Schmitz that they were "deeply concerned about the allegations."

In a letter to the secretary of the Air Force, Allard said that many of the cadets who contacted him claimed their investigative reports were lost, they were not allowed to have a family member or advocate in the room with them while being questioned, and they never knew whether their assailant had been punished.

"Records are missing, there's no way to track data on how many assaults occurred," Allard said. "The academy has not followed our recommendations and we're going to continue to press this until things change."

Secretary Of Air Force To Speak About Alleged Rapes

The secretary of the Air Force will be in Colorado Springs on Thursday. Air Force Secretary James Roche is expected to talk with Air Force Academy cadets and staff about the allegations that female cadets were reprimanded after reporting sexual assaults, the academy announced Tuesday.

Roche (pictured, left) was already scheduled to speak at the academy's National Character and Leadership Symposium before the allegations surfaced. Roche's spokesman Lt. Col. Chet Davis would not comment on what Roche planned to say.

7NEWS Investigates broke the story earlier this month that reported at least five female cadets claimed they were punished for reporting they had been sexually assaulted.

After the 7NEWS Investigates reports surfaced, Roche ordered a special task force to examine how the academy deals with sexual assaults. Team members at the academy on Monday set up a phone line for cadets to report information about alleged assaults that have gone unpunished.

The academy set up a hot line in 1996 to allow cadets to anonymously report assaults. There have been 99 calls reporting some form of sexual assault, from inappropriate touching to rape.

The academy's superintendent, Lt. Gen. John Dallager, has said in written statements that there is zero tolerance for sexual assault at the school and in the Air Force.

Dallager told 7NEWS that he believed the women who reported the rapes but to his knowledge, there have been no cadets who were court-martialed for cadet-on-cadet sexual assault.

Lt. Col. Dewey Ford said more investigators were arriving Tuesday to look into the claims. The team is to wrap up work Friday and may meet with Roche during his visit.

ABC's "20/20" and the New York Times interviewed some of the women after they first talked to 7NEWS Investigates. The ABC interviews may air Friday.