Not only is it unjustified, attacking during a negotiation seriously undermines future negotiations. This is a massive self face punching exercise.
Was there really a negotiation? It seems like US is giving them an ultimatum, stop nuclear enrichment and ballistic missile production or well hit you
Don't fool yourself and others, attacking during negotiation is part of the negotiation.
Israel has even killed a Hamas negotiator in 2024 during deliberations, and attempted to kill another one in 2025.