Related Rule
Australia
Practice Relating to Rule 2. Violence Aimed at Spreading Terror among the Civilian Population
Australia’s Defence Force Manual (1994) states: “Acts or threats of violence primarily intended to spread terror among the civilian population are prohibited.” 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 531; see also Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 955(b).
The manual also states: “Offensive support or strike operations against the civilian population for the sole purpose of terrorising the civilian population [are] prohibited.” 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 554.
Australia’s LOAC Manual (2006) states:
5.21 Civilians. Civilians must be protected from the dangers of military operations. They must not be the object of attack nor of acts or threats of violence which are intended to create terror …
Protection of civilians and civilian objects
5.35 … Acts or threats of violence primarily intended to spread terror among the civilian population are prohibited …
Terrorisation of civilian population
5.59 Offensive support or strike operations against the civilian population for the sole purpose of terrorising the civilian population is prohibited. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, §§ 5.21, 5.35 and 5.59; see also § 9.18.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).
Australia’s War Crimes Act (1945) considers “any war crime within the meaning of the instrument of appointment of the Board of Inquiry [set up to investigate war crimes committed by enemy subjects]” as a war crime, including “murder and massacres – systematic terrorism”. 
Australia, War Crimes Act, 1945, Section 3.