A new law makes it an offence to recruit, use, finance or train mercenaries.
The Mercenary Activities (Prohibition) Bill also makes it an offence to take part in a war, or an act of violence, as a mercenary.
Justice Minister Phil Goff said all the offences would be punishable by up to 14 years' imprisonment and New Zealanders could be prosecuted in New Zealand for acts committed overseas.
The legislation will allow New Zealand to accede to an international convention which has been in force since 2001.
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