i'm maurice dubois. the u.s. is stepping up security in afghanistan after the killing of two american military officers today by an unknown gunman. the officers were shot in the heavily guarded interior ministry in kabul, while in kunduz to the northeast, three people died in a violent protest outside a u.n. compound. it is all part of the turmoil since u.s. troops inadvertently burned copies of the koran earlier this week. mandy clark is in kabul. >> reporter: the shooting erupted at the command-and- control center inside afghanistan's ministry of interior. it should have been the most secure location in the building. sources told cbs news that the two american officers, a colonel and a major, were shot in the head with a pistol at close range. witnesses heard three shots. a colleague ran to the command center, finding the two dead. the gunman had disappeared. there are reports he was an afghan officer who had earlier argued with the americans. later, the taliban claimed responsibility, saying one of its members