Its also important to note that

In many States customary international law – or the practice underlying its rules – can be invoked before national courts and tribunals. In Israel, for example, the Supreme Court delivered a judgment in 2008 concerning restrictions on the flow of fuel and electricity to Gaza. The court referred to customary IHL and the ICRC study which stated that "each party to a conflict is obliged to refrain from disrupting the passage of basic humanitarian relief to populations needing it in areas under its control."