A detail from the UN report:

United Nations 2004

160. The search for an agreed definition usually stumbles on two issues. The first is the argument that any definition should include States’ use of armed forces against civilians. We believe that the legal and normative framework against State violations is far stronger than in the case of non-State actors and we do not find this objection to be compelling. The second objection is that peoples under foreign occupation have a right to resistance and a definition of terrorism should not override this right. The right to resistance is contested by some. But it is not the central point: the central point is that there is nothing in the fact of occupation that justifies the targeting and killing of civilians.