18 § 2441, "War Crimes" provides:

• (a) Offense.--Whoever, whether inside or outside the United States, commits a war crime, in any of the circumstances described in subsection (b), shall be fined under this title or imprisoned for life or any term of years, or both, and if death results to the victim, shall also be subject to the penalty of death.
• (b) Circumstances.--The circumstances referred to in subsection (a) are that the person committing such breach or the victim of such war crime is a member of the Armed Forces of the United States or a national of the United States (as defined in section 101 of the Immigration and Nationality Act).
• (c) Definition.--As used in this section the term 'war crime' means any conduct--
• (1) defined as a grave breach in any of the international conventions signed at Geneva 12 August 1949, or any protocol to such convention to which the United States is a party;
• (2) prohibited by Article 23, 25, 27, or 28 of the Annex to the Hague Convention IV, Respecting the Laws and Customs of War on Land, signed 18 October 1907;
• (3) which constitutes a violation of common Article 3 of the international conventions signed at Geneva, 12 August 1949, or any protocol to such convention to which the United States is a party and which deals with non- international armed conflict; or
• (4) of a person who, in relation to an armed conflict and contrary to the provisions of the Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-Traps and Other Devices as amended at Geneva on 3 May 1996 (Protocol II as amended on 3 May 1996), when the United States is a party to such Protocol, willfully kills or causes serious injury to civilians.