WASHINGTON — Insider attacks in Afghanistan, often referred to as green-on-blue attacks, had been a concern of U.S. military leaders and lawmakers on Capitol Hill long before an Oklahoma soldier and three others were killed in a firefight started by an Afghan police officer Monday in the Wardak province.

Sen. Jim Inhofe, R-Tulsa, asked about such attacks at an Armed Services Committee last fall, and top military leaders have addressed the problem numerous times on Capitol Hill and elsewhere.

At a Senate hearing one year ago, Marine Gen. John Allen, who was commanding NATO forces in Afghanistan, said 52 Americans had been killed and another 68 wounded in insider attacks, such as the one Monday that claimed the life of Staff Sgt. Rex Schad, 25, of Edmond.

Those numbers, Allen said, go back only to 2007, when the military started tracking casualties from green-on-blue attacks. And they were only current through March 2012.

Allen said 13 coalition troops were killed in the first three months of 2012 “at the hands of what appear to have been Afghan security forces.”

Allen said the military believed some of those attacks were motivated in part by the “mishandling of religious materials.” In February 2012, some U.S. troops in Afghanistan burned Korans that they mistook for trash, which set off riots.

According to The Associated Press, 64 coalition troops were killed in 2012 and 95 wounded in insider attacks. The Defense Department said 62 of those killed were U.S. troops.

In September, Allen announced that he had delayed training of 1,000 new recruits for the Afghan Local Police to ensure there was enough time and manpower to recheck the 16,000 police already working. Allen also established more counterintelligence teams in coalition and Afghan formations and created an anonymous reporting system for insider threats. (Agencies)