The investigation of the allegations is being conducted by special agents from the Army's Criminal Investigation Command, the Pentagon said.

Pentagon spokesman George Little said Hagel was notified of the allegations on Tuesday morning by Army Secretary John McHugh. Hagel urged McHugh to ensure the allegations are investigated quickly and dealt with appropriately, he said.

"I cannot convey strongly enough his frustration, anger, and disappointment over these troubling allegations and the breakdown in discipline and standards they imply," Little said in a statement.

Little said the Army and the other military services were in the process of implementing Hagel's directive to re-train, re-credential and re-screen all sexual assault prevention and response personnel and military recruiters.

The investigation of the sergeant came just a week after the head of the Air Force's anti-sexualassault unit was arrested on charges of sexual battery after allegedly groping a woman in a parking lot in a restaurant district not far from the Pentagon.

Lieutenant Colonel Jeffrey Krusinski, 41, was suspended from his duties in the sexual assault response office, and his case is being handled by civilian authorities in Arlington, Virginia, who declined an offer from the military to prosecute the case.

Krusinski's arrest came a day before the Pentagon released its annual report on sexual assault in the military, a study that estimated the number of sex crimes involving military personnel soared by 37 percent to 26,000 in 2012, from 19,000 in 2011.

The crimes ranged from rape to abusive sexual contact.

The military's problem with sexual assault has prompted some lawmakers to call for the crime