Two days after a major terrorist attack on a city in its territory, State A launches missile strikes against certain areas and facilities in State X. State A alleges that these strikes have been carried out in lawful exercise of its right of self-defence as the targets in State X harbour the terrorist group, Faction Q, that it says was responsible for the attack on State A.

Shortly afterwards, State A also launches missile strikes against targets in State Y and State Z. It alleges that State Y has provided financial and logistical support to Faction Q and has declared political support for Faction Q's attacks on State A. In State Z, State A attacks facilities that it says are being used to produce chemical and biological weapons that will be made available to terrorist groups linked to Faction Q, and which it suspects may be used to attack State A in the future.

Is the use of force by State A in these instances lawful?