WASHINGTON - The State Department on Saturday confirmed that Tariq Khdeir, an American citizen, has been detained by Israeli authorities, issuing harsh words over the possible use of "excessive force" on the 15-year-old relative of a Muhammad Abu Khdeir, a Palestinian teenager also killed this week in a possible revenge killing.An American official from the US consulate general in Jerusalem visited the boy in custody on Saturday. He is being held in Jerusalem."We are profoundly troubled by reports that he was severely beaten while in police custody and strongly condemn any excessive use of force," State Department spokeswoman Jen Psaki said in a statement. "We are calling for a speedy, transparent and credible investigation and full accountability for any excessive use of force."Images of the boy's wounds spread quickly through social media after the incident, as did a video of the alleged assault by Israeli forces."We reiterate our grave concern about the increasing violent incidents, and call on all sides to take steps to restore calm and prevent harm to innocents."The State Department did not call for Khdeir's immediate release.The Justice Ministry late Saturday night said it was opening an investigation into the beating after videos of the beating have gone viral.Khdeir, 15, of Tampa, Florida was allegedly beaten and detained by Israeli security forces, according to Palestinian media reports.Khdeir is the Palestinian-American cousin of Muhammad Abu Khdeir, who was murdered on Wednesday in a suspected revenge attack following the discovery of the bodies of the three abducted Israeli teens.A video being circulated by human rights groups allegedly shows two Israeli police officers kicking and beating the high school student. Palestinian media published photos depicting a boy with a badly bruised face, whom they claim is Khdeir.The director of the Council on American-Islamic Relations of Tampa told a local Florida television station that the video shows security forces "stomping on his face," and that Khdeir had been detained in Jerusalem following his participation in riot.Israel Police spokesman Micky Rosenfeld was quoted by the New York Times as saying that the footage was "edited and biased," and that it "did not represent the scope of events."Rosenfeld told the Times that Tariq was one of six people who had been arrested Thursday after clashes in which 15 police officers were injured.