Supposedly friendly Afghan security forces have attacked U.S. and coalition troops 45 times since May 2007, U.S. officials say, for the first time laying out details and analysis of attacks that have killed 70 and wounded 110.

In testimony prepared for delivery Wednesday to the House Armed Services Committee, defense officials said that in most cases the Afghans 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.

Such insider attacks by Afghan security forces have been on the rise, punctuated by the Jan. 20 shooting of four French troops by an Afghan soldier, which prompted France to halt its training program and threaten to withdraw its forces from Afghanistan earlier than planned. 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.

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 disagreed on exactly what happened in the killing. A spokesman for the international military force said Afghan soldiers detained the gunman after he attacked NATO troops Tuesday night. Afghan National Army commander Sayed Malluk confirmed the shooting, but said the Afghan soldier told investigators it was an accident.

The U.S. defense officials' testimony, obtained by The Associated Press in advance of Wednesday's hearing, lays out the screening process for Afghan nationals who are brought in to provide security for U.S. forces. And it includes improvements in the program made after an attack at Forward Operating Base Frontenac in March 2011 that killed two U.S. soldiers and wounded four others. The base is in Kandahar Province in southern Afghanistan, and lawmakers have been demanding details about the incident.

"The insider threat is an issue of increasing significance to coalition forces and Afghan National Security Forces operating in Afghanistan," the defense officials said. "It creates distrust between our forces and their Afghan counterparts during a critical juncture in Afghanistan."

Among the officials scheduled to present the data to the committee are Deputy Assistant Defense Secretary David Sedney and Brig. Gen. Stephen Townsend, who is the Pentagon's director of the Pakistan-Afghanistan coordination group.

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 report to Congress also includes details about the March 2011 incident that 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 but the allegation was unsubstantiated. And Tundra did not pass that information along to U.S. military authorities prior to the Frontenac incident.

As a result of the attack, the military issued a request for corrective action — a formal action taken against contractors that requires them to submit plans to fix the problems found. Tundra submitted a plan, which was accepted by the military, and the case was closed, although the contract will continue to be audited.

Since then 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.