Putting aside the apparent lack of congressional approval for the strike, a legal requirement of undertaking the use of force in the U.S. legal system, would appear that the Trump Administration acted outside the remit of international law. There is no question that actions committed by Soleimani and the forces he commanded were cruel and directly targeted American personnel and soldiers in the past. Soleimani was designated a terrorist in 2011 by the U.S. government, but he was still an important official in the Iranian government. As Karen Greenberg, Director of the Center on National Security at Fordham University Law School, says, “you can’t take aim at an official inside a government and say that is not a war.”

However, according to the Trump Administration, the drone strike on Soleimani was legal and in accordance with international law. The justification for the strike is based on the perceived imminence of an attack by Iran, thus making the drone strike a defensive measure. Trump Administration officials have said that an attack on the U.S. by Iran was a matter of days away, so they had to act accordingly in order to protect “hundreds of lives.” The use of force is prohibited in Article 2(4) of Charter of the United Nations, with the exception of acting in self-defense found in Article 51. Article 51, however, states that self-defense is only justified in response to an armed attack, and not in response to a hypothetical armed attack.

The evidence of an “imminent threat” from Iran is not particularly convincing either. While evidence of Soleimani “actively plotting” an attack – as claimed by Secretary of State Mike Pompeo in an interview with CNN – is most likely highly classified, intelligence experts remain unconvinced. The U.S. says that the Soleimani-led Quds Force had backed the Iraqi militia that launched numerous attacks on American personnel, including the attempt to storm the U.S. Embassy in Baghdad in 2019. However, this does not amount to proof of a further attack on the U.S. which could justify a defensive strike on Iranian government officials. Hina Shamsi, Director of the National Security Project at the American Civil Liberties Union, notes that “the very limited circumstances in which use of force might be permitted…quite simply haven’t been met here.”

The Trump Administration’s decision to carry out the targeted strike on Soleimani follow a precedent established by the Obama Administration. Dr. Ralph Wilde, an expert in Public International Law from University College London, points out that since the attacks on September 11, 2001, the U.S. has utilized a definition of self-defense that justifies targeted strikes in response to the threat of future and hypothetical attacks, or “when the attack is being planned, but is not imminent.” This was the justification the Obama Administration used to legitimize drone strikes in Pakistan.

Targeted killings carried out by the U.S. in other states are problematic as well, as United Nations Special Rapporteur on Extra-Judicial Executions Agnes Callamard notes. The Trump Administration has used targeted killings elsewhere, but most recently in the raid that killed Abu Bakr al-Baghdadi, the head of ISIS. However, unlike Soleimani, al-Baghdadi was not a member of a foreign government and evidence of al-Baghdadi’s crimes were spread across Syria and Iraq. In the case of Soleimani, evidence of crimes is far less clear given the lack of access to Iran. While targeted killings are permitted under international law, very strict conditions are attached. The self-defense argument is only acceptable under Article 51 if there is evidence of an imminent armed attack. Moreover, international law clearly stipulates that actions of self-defense must be proportionate to the threat faced.  Hence, even if Soleimani posed an imminent threat to American lives, killing him in Iraq is not a proportional response.

The immediate response of the Iranian government has been violent. On January 8th, Iran fired rockets on Iraqi military compounds housing U.S. military forces, resulting in the death of Iraqi citizens and accidentally shot down a Ukrainian passenger aircraft in Iranian airspace immediately after. These responses are evidence that the extrajudicial killing of Soleimani has many implications. For one, as a result of the death of al-Muhandis with Soleimani, the tenuous relationship the U.S. has maintained with Iraq since the early 2000s has been rocked. Further, according to the principle of self-defense in Article 51, Iran may have justification to retaliate in kind against the United States.