If there is a government that has a monopoly on the lawful use of force and some private organization comes along and decides that it is going to violate that monopoly arrangement, then yes. They're criminals. If we are talking about an ungoverned space where there is no lawful monopoly on the use of force then the private organization is not necessarily criminal in nature (though it probably is violating some international law), but it almost certainly uses tactics very similar to those employed by a criminal organization.
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