A simple question about Suleimani's killing: was it legal?

<50% It is unprecedented since the Second World War for one state to claim that it had the right to assassinate senior officials in another

Many questions are raised by the death of Iranian commander Qassem Suleimani. Had Donald Trump, the US president, thought through all the repercussions for the region and beyond before ordering the drone strike that killed him? Unfortunately, that seems unlikely. Will it make America safer? Former US president Barack Obama's national security adviser Susan Rice thinks not; and neither, evidently, does the US state department, which has advised its citizens to leave Iraq immediately.

I will leave the immediate future to others to debate. My question about Suleimani's killing is simple: was it legal?

Some might ask why it is worth bothering with such pettifogging niceties. Was Suleimani not, like Osama bin Laden and Abu Bakr Al Baghdadi, responsible for thousands of deaths? Did he not deserve the same himself? As commander of the Quds Force of the Islamic Revolutionary Guard Corps and arguably chief executor of Iran's aggressive interventions abroad for decades, including its military backing of Bashar Al Assad in Syria and Hezbollah in Lebanon, his responsibility is undisputed.

The difference is that Bin Laden and Al Baghdadi were outlaw terrorists, and it is doubtful that either could have been taken alive, even if there had been any desire to do so; Al Baghdadi blew himself up when cornered by anti-ISIS forces, and Bin Laden had weapons in his room when he was shot to death by US Navy Seals in his hideout in Pakistan in 2011.

The IRGC might have been designated a terrorist organisation by the Trump administration but that was only last April. And Suleimani, by contrast, had been a very high-ranking general in Iran for more than 20 years. Many believe that he was the second-most important figure in Iran, more powerful than the elected president.

Even if the attack was to prevent imminent attacks on US personnel, as the White House has put forward as justification – which is disputed – it has been unprecedented since the Second World War for one state to claim openly that it had the right to assassinate senior officials in another. Agnes Callamard, the United Nations special rapporteur on extrajudicial, summary or arbitrary killings, was clear. The targeted attack on Suleimani and his companions, she wrote on Twitter, was likely "unlawful" and violated international human rights law. "Outside the context of active hostilities, the use of drones or other means for targeted killing is almost never likely to be legal."

As Professor Patrick Porter, a leading international relations academic, put it in the aftermath of the attack: "You can argue for a special prerogative to carry out such killings. Or you can argue for a rules-based order that binds all states. But doing both at the same time... looks just plain ridiculous." He pointed out that using the same logic, Russia could have justified assassinating CIA officials in the 1980s, on the grounds that they were sponsoring jihadist opponents of Afghanistan's Soviet-backed government.