Chapter 16. Genocide, crimes against humanity and war crimes
Section 103. War crimes against persons
Any person is liable to punishment for a war crime who in connection with an armed conflict
(e) takes a protected person hostage,
Grave breaches - IAC
Taking of hostages - IAC
Taking of hostages - NIAC
Violations of laws and customs - IAC
Serious violations of Common Article 3 - NIAC
EDIT.