WASHINGTON - The U.S. killing last week of top Iranian general Qassem Soleimani has sparked a fierce debate about the legality of the strike - and a subsequent Iranian counterstrike on two military bases in Iraq - under international law.
In an ironic twist to the crisis triggered by Soleimani's death, Jan. 3, both Washington and Tehran have invoked the same international legal principle enshrined in the United Nations Charter: a country's right of self-defense.
In separate letters to the U.N. Security Council Wednesday, U.S. Ambassador Kelly Craft and Iranian envoy Majid Takht-Ravanchi described the tit-for-tat attacks as exercises in self-defense in accordance with the U.N. Charter.
But engaging in such rhetoric doesn't necessarily justify a state's use of force, said Geoffrey S. Corn, a retired U.S. Army Judge Advocate General (JAG) officer who is now a professor at South Texas College of Law Houston.
"What both the United States and Iran were required to do under international law is make a reasonable assessment based on all the information they had available, not that they had just been the victim of a prior attack but that those prior attacks coupled with all the other intelligence indicated that they were about to become the victim of a subsequent unlawful, armed attack," Corn said.
Whether the United States and Iran were justified in carrying out the strikes remains the subject of controversy even as tensions between the two countries have diminished.
While U.S. officials such as National Security Adviser Robert O'Brien insist they have "strong evidence" of Iranian plans for attacking U.S. forces, critics say the administration has yet to make a compelling case for killing Soleimani.
House Speaker Nancy Pelosi described the Soleimani strike as "provocative and disproportionate" ahead of a vote Thursday on a resolution directing Trump not to use the military to engage in hostilities with Iran.
What does international law say about the strikes?
The pertinent international law here is the United Nations Charter. Under Article 51 of the charter, member states have the right of self-defense in the event of "an armed attack." That language has been widely interpreted to encompass taking action in order to prevent an imminent armed attack. The operative word here is imminent. Once the threat has passed, use of force can't be justified. There are two other requirements: that the use of force be necessary and that the scope of the force be proportionate to reduce the threat, Corn said.
There is an important difference between self-defense and retaliation under international law. While self-defense - or acting in response to an imminent attack - is lawful, retaliation is not. "Self-defense never authorizes you to take measures in retribution or revenge or reprisal," Corn said.
What is the U.S. justification?
In seeking to justify President Trump's order to kill Soleimani with a drone strike near Baghdad airport, U.S. officials have cited a series of recent Iranian hostile acts against U.S. interests, including an attack on an Iraqi military base that killed a U.S. military interpreter last month. But officials have been careful to cast the strike as a defensive measure against future Iranian attacks.
Just how imminent the threat was remains unclear.
The Pentagon initially avoided the word imminent in describing the Iranian threat, saying the strike was "aimed at deterring future Iranian attacks." As Democratic lawmakers and other critics pressed the administration for a justification, Trump and top administration officials subsequently took to describing the Iranian threat as imminent, suggesting administration legal advisers required policymakers to make a judgment about its imminence.
What authority does the U.S. president have to use military force?
While the U.S. invoked the right of self-defense in killing Soleimani, some scholars believe the president has the legal authority to carry out such an action without relying on international law.
The U.S. Constitution gives Congress the power to declare war. But as commander-in-chief, the president enjoys broad constitutional authority to use military force overseas in order to protect American interests. This authority has long been recognized. Even the War Powers Resolution approved Thursday by the House of Representatives, 224-194, recognizes the president's power to use force during "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces."
What about Iranian justification?
Iran's foreign minister, Mohammad Javad Zarif, described the Iranian missile strikes against two Iraqi bases housing American troops as "proportionate measures in self-defense under Article 51 of UN Charter."
"We do not seek escalation or war, but will defend ourselves against any aggression," he tweeted Wednesday.
Ravanchi, the Iranian ambassador to the U.N., wrote in his letter to the Security Council that Iran "exercised its right of self-defense" by taking a "measured and proportionate military response targeting an American air base in Iraq."
The sober legal language stands in stark contrast to the more incendiary rhetoric of Iranian leaders who have by turns described the Iranian strike as "fierce revenge" and "forceful revenge," which would be illegal under international law.