The US government is no stranger to the dark arts of political assassinations. Over the decades it has deployed elaborate techniques against its foes, from dispatching a chemist armed with lethal poison to try to take out Congo's Patrice Lumumba in the 1960s to planting poison pills ... in the Cuban leader Fidel Castro's food. But the killing of General Qassem Suleimani, the leader of Iran's elite military Quds Force, was in in a class all its own. Its uniqueness lay ... in the brazenness of its execution and the apparently total disregard for either legal niceties or human consequences. The US simply isn't in the practice of assassinating senior state officials out in the open," said Charles Lister, senior fellow at the Middle East Institute in Washington. Donald Trump's gloating tweets over the killing combined with a sparse effort to justify the action in either domestic or international law has led to the US being accused of the very crimes it normally pins on its enemies. Iran's foreign minister, Mohammad Javad Zarif, denounced the assassination as an "act of international terrorism". Mary Ellen O'Connell, a professor of international law at the University of Notre Dame, draws a direct line between earlier US administrations and the convention-shredding unpredictability of Trump. "Since Obama there has been a steady dilution of international law," O'Connell said. "Suleimani's death marks the next dilution - we are moving down a slope towards a completely lawless situation." O'Connell added that there was only one step left for the US now to take. "To completely ignore the law. Frankly, I think President Trump is there already - his only argument has been that Suleimani was a bad guy and so he had to be killed."