Related Rule
Israel
Practice Relating to Rule 4. Definition of Armed Forces
According to Israel’s Manual on the Laws of War (1998), “soldiers serving in the army (regular and reserve) or in well-ordered militia forces (e.g. the SLA or the State National Guards in the United States)” must fulfil four conditions:
1. The combatants must be led by a commander and be part of an organization with a chain of command.
2. The combatants must bear a fixed recognizable distinctive sign that can be recognized from afar.
3. The combatants must bear arms openly.
4. It is incumbent on combatants to behave in compliance with the rules and customs of war. 
Israel, Laws of War in the Battlefield, Manual, Military Advocate General Headquarters, Military School, 1998, pp. 47–48.
In 2009, in a report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009 (the “Gaza Operation”, also known as “Operation Cast Lead”), Israel’s Ministry of Foreign Affairs stated:
Whereas members of a civilian police force that is solely a civilian police force, who have no combat function are not considered combatants under the Law of Armed Conflict, international law recognises that this principle does not apply where police are part of the armed forces of a party. In those circumstances, they may constitute a legitimate military target. In other words, the status of the Palestinian “police” under the Law of Armed Conflict depends on whether they fulfilled combat functions in the course of the armed conflict. The evidence thus far is compelling that they are. 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, § 238.
[footnote in original omitted; emphasis in original]