KABUL — The policewoman who killed an American contractor in Kabul is a native Iranian who came to Afghanistan and displayed ‘‘unstable behavior’’ but no known links to militants, an Interior Ministry spokesman said Tuesday.

The policewoman, identified as Sergeant Nargas, shot 49-year-old Joseph Griffin, of Mansfield, Ga., on Monday, in the first such shooting by a woman in a spate of insider attacks by Afghans against their foreign allies.