Afghan soldier kills three Americans KABUL - An Afghan soldier opened fire on U.S. troops in eastern Afghanistan on Saturday after arguing with one of the Americans, killing two service members and a civilian, U.S. and Afghan officials said. The confrontation marked the deadliest insider attack in the country this year and added to the death toll from an intense fighting season, which U.S. and Afghan officials are watching closely for indicators of the Taliban's resilience as American troops accelerate their withdrawal. In a separate incident Saturday, an Italian captain was killed in a grenade attack in western Afghanistan. The insider attack occurred shortly after noon in Paktika province, which borders Pakistan, after an Afghan soldier got into a verbal dispute with an American service member, according to an account by the provincial governor's office. The Americans returned fire, killing the Afghan gunman, provincial officials said. Afghan and American officials are investigating the incident, but provincial authorities said they had found no evidence that the Afghan soldier had links to the insurgency. The U.S. military said an Afghan was detained after the shooting, but provided no details about the circumstances. Insider attacks became a paramount concern for the U.S.-led coalition here last year, when Afghan troops killed 64 foreign military personnel and civilians in 48 incidents. Far fewer have occurred this year. Before Saturday's attack, five coalition members had been killed in so-called "green on blue" attacks. U.S. military officials went to great lengths to study insider attacks last year after their prevalence began to poison the military partnership at the heart of the U.S. strategy for winding down the Afghan war. Investigators found that relatively few such attacks could be traced to the insurgency, with a high percentage stemming from fights over cultural differences. Earlier Saturday, an Italian military training team was returning to its base in Farah province when it came under attack. One soldier was killed and three wounded in the blast, according to the Italian Defense Ministry. The Taliban did not assert responsibility for that attack but hailed it in a statement. According to local reports, its statement, which could not be corroborated, said an 11-year-old child had lobbed a grenade at the Italians. "This incident clearly shows the utter hatred of Afghans toward the foreign invaders who have occupied our land in the past decade," the statement said. Saturday's military casualties came two days after seven Georgian troops were killed in a truck bombing in southern Afghanistan. Julie Tate in Washington contributed to this report.