More than 150 Afghan troops that were in the United States for training have gone absent without leave, or AWOL, since 2006, according to a new audit from the Pentagon.

"[T]he limited vetting of Afghan trainees, and the restrictions of the investigatory and asylum processes, may pose a security risk to the United States when trainees go AWOL," the inspector general report said.

Most of those who abandoned their posts did so in three different years that were marked by particularly high levels of violence, according to a report released Friday by the special inspector general for Afghanistan reconstruction. Some reported that their families had been threatened by the Taliban after they left for the U.S.

But the disappearances also reveal a weakness in how federal officials oversee the training program, the report suggested.

"[I]ssues with interagency coordination have hindered investigatory efforts to locate AWOL trainees," the inspector general found.

The absentee Afghan troops represent just a sliver of the 253,977 foreign military trainees who have come to the U.S. in recent years. About 2,500 of those people were from Afghanistan. But the Afghan forces furnished 152 of the 320 foreign military trainees who went absent without leave upon arrival in America.

The report prompted alarm in Congress, where lawmakers worry about both the risk of terrorism and how the loss of the trainees undermines the effectiveness of the Afghan military to fight the Taliban and other threats.

"The majority of these Afghan military trainees have been located, but the fact that any of them remain unaccounted for is deeply concerning and it's important we get more information on how this happened and what's being done to locate these individuals," Sen. Claire McCaskill, D-Mo., the top Democrat on the Homeland Security and Government Affairs panel, said Friday.

Three of those individuals "were no longer AWOL or returned to their U.S.-based training," but the other results are more mixed. "The status of the 152 Afghan trainees who went AWOL included: 70 who fled the United States; 39 who gained legal status in the United States; 27 who were arrested, removed, or being processed for removal from the United States; 13 who were still AWOL or remained unaccounted for," the report found.

Those people could be dangerous, according to U.S. Immigration and Customs Enforcement officials who consulted with the inspector general.

"Although we are not aware of any acts of terrorism or similarly serious acts involving Afghan trainees who have gone AWOL, such cases are considered by [ICE's counterterrorism team] to be high risk because they involve militarily trained individuals of a fighting age who have demonstrated a ‘flight risk,' and have little or no risk of arrest and detention for absconding from training," the report said.

The inspector general suggested that the Afghan trainees undergo a stricter vetting process to see if they plan to return to their home country, but the State Department rejected the proposal.

"We maintain that in-person interviews may provide valuable information regarding the likelihood of a trainee to abscond from training in the United States, and additional information (e.g. the names and addresses of friends and family members living in the United States) that, if shared with ICE, may be helpful in their investigative work," the inspector general insisted.