The U.S. military provided sweeping details Wednesday of the problem of insider attacks by Afghan security forces against U.S. and other coalition troops, prompting lawmakers to call the screening process for Afghan forces "tragically weak."

Reacting to Pentagon data showing that 75 percent of the more than 45 insider attacks since 2007 occurred in the last two years, House members demanded that the U.S. intervene more quickly to suspicions that someone might be a threat.

"The screening and vetting has been tragically weak in picking up signs of threats after the Afghans joined either the Afghan National Security Force, or a private security contractor," said House Armed Services Committee Chairman Howard "Buck" McKeon, R-Calif.

Defense officials said they have beefed up the vetting process, but warned that safeguards can be improved but there is no way to totally eliminate the problem.

Wednesday's hearing marked the first time defense officials have laid out the problem in such detail, prompted by the Jan. 20 shooting of four French troops by an Afghan soldier.

France reacted by halting its training program and threatening to withdraw its forces from Afghanistan earlier than planned. And the incidents further erode support for the increasingly unpopular war in Afghanistan, and add more complications to the already difficult mission of U.S. forces.

"We can do more," said the committee's ranking Democrat, Rep. Adam Smith of Washington, adding that the military must "monitor for problems and err on the side of interceding sooner, rather than later."

He said if someone isn't deemed 100 percent safe, then they should not be given a gun and placed so close to coalition troops.

According to the Pentagon, most of the attackers acted out of personal motivation and were not controlled or directed by insurgent groups. The second most common circumstances involved insurgents impersonating or infiltrating Afghan security forces.

The figures do not include an incident Wednesday in which an Afghan soldier shot and killed a NATO service member in southern Afghanistan. International forces and the Afghan army disagree on exactly what happened in the killing, with Afghans suggesting it may have been an accident.

U.S. defense officials laid out the screening process for Afghan nationals who are brought in to provide security for U.S. forces. The programs include some improvements made after an attack at Forward Operating Base Frontenac in March 2011 that killed two U.S. soldiers and wounded four others.

Since that killing, the U.S. has directed commanders to conduct random checks on private security companies to ensure that all of their personnel are properly screened, including all of the biometric requirements. Commanders also have to do weekly biometric screenings of local nationals to compare against watch lists.

The parents of a soldier killed in the March 2011 incident _ Spc. Rudy Acosta _ attended the hearing. Acosta was from McKeon's congressional district.

In a letter to the committee, read by McKeon, Acosta's father said that his family and the nation believe that only U.S. troops, and not private contractors, should be used to provide security for bases.

Gary J. Motsek, a deputy assistant defense secretary, told the panel that using U.S. forces, rather than Afghans, to provide security would require taking 20,000 troops out of their combat roles. He added that while the incidents are unacceptable, it's not likely they can be eliminated.

Deputy Assistant Defense Secretary David Sedney, meanwhile, noted that partnering with Afghan forces is a critical element of the U.S. military strategy that is allowing forces to make some progress in Afghanistan.

Asked about other possible steps the U.S can take to reduce the problem, Brig. Gen. Stephen Townsend said commanders can decide to post their own guards or they can assign someone to serve as a "guardian angel."

That person's sole responsibility, said Townsend, who is the Pentagon's director of the Pakistan-Afghanistan coordination group, would be to serve as an observer during meetings, training sessions or other events, and watch for and quickly react to any unusual activity.

While there have been some instances of insurgents secretly joining the Afghan security forces, officials said it is difficult to determine how often that has happened because the infiltrator often remains undetected. Insurgents can easily disguise themselves as Afghan security forces and have been doing so more often, the military said, noting that the attackers simply obtain and wear Afghan uniforms.

Overall, however, officials said most attacks have come from members of the Afghan forces "acting intentionally yet independently" without any direct guidance from outside insurgent groups. They are generally spurred by personal motivations, grievances, ideological differences or even combat stress.

Until now, Pentagon officials had not released figures on the number of incidents. But the officials said there have been 42 incidents involving Afghan security forces and three others involving private security company personnel. In most cases the assault involved small arms fire.

The defense officials also provided some details of the March 2011 incident. The shooting involved an Afghan man hired by the private security contractor Tundra, which provides protection at nine installations in Afghanistan.

Security companies that hire Afghans are required to carry out an in-depth vetting process that includes verifying applicants' identities, work history, address and other personal information, as well as police checks, fingerprinting and other biometric information such as iris scans and photographs. The contractors are also required to report individuals who turn out to be security risks.

According to the defense officials, Tundra's official records had indicated the company had investigated the man involved in the Frontenac attack as a possible threat. The man was fired, but the allegation was later unsubstantiated, so the man was not flagged as a threat, and was rehired.