WASHINGTON — The US Air Force said Thursday at least 31 female cadets were victims of alleged sexual assault by military instructors in a widening scandal at the service's training command.

General Edward Rice, commander of Air Education and Training Command, said authorities are investigating 12 male training instructors for suspected sexual misconduct at Lackland Air Force Base near San Antonio, Texas.

He said nine of the 12 instructors were from the 331st Training Squadron, and that the problem appeared to be confined mostly to that unit.

The commander of the squadron was relieved of his duty earlier this month over the allegations, Rice told a news conference at the Pentagon.

It was unclear how long sexual misconduct had been going on at Lackland but the Air Force believed the abuses dated back to 2009, he said.

Rice said "we have identified some 31 victims and are actively seeking any others that may have been affected by this."

He also said an Air Force officer outside the training command, Major General Margaret Woodward, would carry out an independent review looking at how his command has handled the scandal.

One trainer, Staff Sergeant Peter Vega-Maldonado, has pleaded guilty to having an inappropriate relationship with a trainee, and also provided testimony that he had improper relations with 10 cadets.

The Air Force strictly bans any personal relationship between instructors and cadets.

Another trainer faces charges of rape and sexual assault and his trial is due to begin next month.

Lawmakers have voiced alarm over the allegations at Lackland as well as a broader problem of sexual assault inside the military.

Defense Secretary Leon Panetta has launched new initiatives to try to tackle the problem, but activists and former officers say thousands of cases go unreported as young service members are afraid of jeopardizing their careers.

At the Air Force briefing, Rice said the vast majority of the service's 500 training instructors perform their jobs with great skill and "no one is more angry and disappointed than they are that a relatively small number of their cadre has cast a shadow over the entire program."

"We are all committed to doing everything possible to investigate those allegations, to take care of the victims, to hold the perpetrators accountable, and to fix any institutional problems that may have facilitated this completely unacceptable behavior," he said.