The term “threat” refers to a government's announcement of an act of violence for the purpose of intimidating another government into changing its policies. Under the Charter, only the Security Council is qualified to make such threats. Every other threat of force is unlawful.
It should also be understood that "threat" within the meaning of Article 2(4) must be understood in a restrictive sense. Hostile statements that are common between antagonistic countries, especially when they're uttered by officials who do not have the constitutional authority to materialize them, do not carry the same legal weight as potent military threats directly issued in a particular context (for the purpose of influencing negotiations) by top officials who actually have the power to order military operations.
Watching the highest political authorities of Israel and the United States so impetuously violate a fundamental rule of international law is on its own very alarming. It signals to Iran and the international community that the West is not willing to play by the rules. It also greatly undermines the credibility and impartiality of all international organizations involved in the negotiating process.
Some would rightly argue that if any other state had so blatantly breached such a central bedrock of the post-UN charter international order, the Security Council or, at least, the Secretary General of the United Nations would have certainly issued a strong condemnation in reply.
Second, and more important, according to a well-known principle of international law, an agreement that is obtained through duress and coercion is considered invalid. The 1969 Vienna Convention on the Law of Treaties – which codifies some of the most fundamental norms in the field – is very clear on the subject. Its Article 52 specifically renders void any international agreement “which has been procured by the threat or use of force in violation of the principles of international law.”