The circumstances leading to a breach of international legal obligation can be best accessed by referring to the rules of customary international law. These rules have been codified in the draft Articles on the Responsibility of States for Internationally Wrongful Acts by the International Law Commission. They provide good evidence as to what constitutes customary international law and are closely followed by States.
The basic understand is that a state is internationally responsible for every wrongful act it commits which is done under its umbrella. Before holding a state responsible for a breach, it has to be ensured that the “wrongful act” committed is directly attributable to the state. Also, it has to be a breach of an international obligation of that State. As a general rule, the conduct is attributable to a State when it is committed by the State’s organs of government or its agents. By “agent”, it is meant to include persons or entities who act under the direction, instigation or control of those organs. Again, persons or entities may be organs if they act in the manner of organs, for instance, police forces.
It is to be noted that purely personal acts of persons or entities cannot be attributed to a State and where these persons act for personal motives or in bad faith, a government is not responsible for their actions under international law. An agent who, for example, has a personal grudge against a foreign national and assaults him in an altercation at a cafe may have committed a crime but his government is not in breach of its obligation to the foreign national. This however is not the rule where a person or entity is acts in his capacity as agent. Article 7 lays states that:
“The conduct of an organ of a State or of a person or entity empowered to exercise elements of the governmental authority shall be considered an act of the State under international law if the organ, person or entity acts in that capacity, even if it exceeds its authority or contravenes instructions.”
This is a strict rule which effectively means the illegality, the excessive nature or negligence of the agent’s conduct will not negate the responsibility of the State. The justification behind the rule is that it is impossible for a State to evade international responsibility by a provision in its domestic law, which would in this case be the law that makes the agent’s act ultra vires. Hence, when an agent acts in a way which leads to a breach under international law, under ordinary circumstances his State becomes liable if the agent was acting in his official capacity regardless of whether his actions were in conflict with or in excess of his instructions and regardless of whether the agent was negligent or acting in bad faith. Furthermore, a State may therefore be responsible even if it attempts to stop the agent or even if it is unaware of the agent’s actions.
See, Draft Articles on the Responsibility of States for Internationally Wrongful Acts, 2001 http://untreaty.un.org/ilc/texts/instruments/english/commentaries/9_6_2001.pdf accessed on 15.04.13
 Mallen, RIAA, vo. V, p.516 (1929)
 See, http://untreaty.un.org/cod/avl/ha/rsiwa/rsiwa.html accessed on 15.04.13
 Petroplane Inc. v. Iran (1991) 27 Iran-US CTR 64 at 92