The UN special rapporteur on extrajudicial killing on Friday said the President Trump-approved drone strike against Qassim Soleimani, Iran’s top general, violated international human rights law.

In a lengthy Twitter thread, Agnès Callamard said that “outside the context of active hostilities, the use of drones or other means for targeted killing is almost never likely to be legal,” adding that the US would need to prove the person targeted constituted an imminent threat to others.

She also took issue with the justification for using drones in another country on the basis of self-defense.

“Under customary international law States can take military action if the threatened attack is imminent, no other means would deﬂect it, and the action is proportionate,” she wrote.

“The test for so-called anticipatory self-defense is very narrow: it must be a necessity that is ‘instant, overwhelming, and leaving no choice of means, and no moment of deliberation.’ This test is unlikely to be met in these particular cases,” she added.

Callamard noted that “an individual’s past involvement in ‘terrorist’ attacks is not sufficient to make his targeting for killing lawful.”

The French human rights expert also criticized the Pentagon’s statement about the airstrike.

“It mentions that it aimed at ‘deterring future Iranian attack plans.’ This however is very vague. Future is not the same as imminent which is the time based test required under international law,” she wrote.

“Overall, the statement places far greater emphasis on past activities and violations allegedly commuted by Suleimani. As such the killing appears far more retaliatory for past acts than anticipatory for imminent self defense,” Callamard continued.

“The statement fails to mention the other individuals killed alongside Suleimani. Collateral? Probably. Unlawful. Absolutely,” she added.

Also killed in the strike was Iraqi militia commander Abu Mahdi al-Muhandis and his son-in-law Mohammed Rida al-Jaberi.