Callamard stressed that denunciations from the international community, as important as they are, do not constitute a satisfactory response.
"The moral voice of UNSG [U.N. Secretary-General] AntonioGuteres matters a great deal in times of crisis. But messages and bilateral exchanges are not enough," the rapporteur tweeted in response to Guterres' call for the de-escalation of military tensions between the U.S. and Iran.
Callamard then urged Guterres to “activate Article 99 of the U.N. charter and establish an impartial inquiry into [the] lawfulness of Soleimani's killing and events leading up to it."
By means of Article 99, “the secretary-general may bring to the attention of the Security Council any matter which in his opinion may threaten the maintenance of international peace and security.”
Callamard already tweeted last week that the U.S. drone attack against Soleimani which occurred Friday in Baghdad, Iraq, was in all probability carried out in breach of international law. The rapporteur’s comments were broadly shared by other legal specialists.
"Lawful justifications for such killings are very narrowly defined and it is hard to imagine how any of these can apply to these killings," Callamard added.
U.S. President Donald Trump justified the move that put a whole region on the brink of war, by stating that Soleimani was plotting "imminent and sinister attacks on American diplomats and American personnel, but we caught him in the act and terminated him."
Yet the White House has to present any evidence to support its version of the events and its self-defense arguments.
Secretary of State Mike Pompeo was unable during a news conference Tuesday to give an exact or specific example of the allegedly imminent threat that authorized Soleimani's murder.
Another problematic concern is related to the question of Iraq’s consent, as the strike was carried out on its soil, and claimed the life of Iraqi Commander Abu Mahdi al-Muhandis.
The Iraqi government has called the attack a bold violation of its sovereignty, and members of the Parliament passed a non-binding resolution calling for U.S. troops to leave the country.
U.S. forces are still in Iraq under the announced purpose of fighting the Islamic State group (ISIS) and to train Iraqi forces.
Although the U.S. might argue that their presence sanctioned by Iraq is a form of consent and gives them the right to protect their interests and personnel inside the country, some experts like professor of public international law at Oxford University Dapo Akande, say that, in practice, the terms of the agreement to host U.S. forces would not extend to the execution of such an attack.