After the United States bombed Iran’s three nuclear facilities on Sunday, US President Donald Trump said its objective was a “stop to the nuclear threat posed by the world’s number one state sponsor of terror.”

US Defense Secretary Pete Hegseth echoed this justification, saying:

The president authorised a precision operation to neutralize the threats to our national interest posed by the Iranian nuclear program and the collective self-defence of our troops and our ally Israel.

Is this a legitimate justification for a state to launch an attack on another?

I believe, looking at the evidence, it is not.

Was it self-defense?

Under the UN Charter, there are two ways in which a state can lawfully use force against another state:

• the UN Security Council authorizes force in exceptional circumstances to restore or maintain international peace and security under Chapter 7
• the right of self-defense when a state is attacked by another, as outlined in Article 51.

On the first point, there was no UN Security Council authorisation for either Israel or the US to launch an attack on Iran to maintain international peace and security.

The Security Council has long been concerned about Iran’s nuclear program and adopted a series of resolutions related to it. However, none of those resolutions authorised the use of military force.

With regard to self-defense, this right is activated if there is an armed attack against a nation. And there’s no evidence of any recent Iranian attacks on the US.

There have been incidents involving attacks on US assets by Iranian-backed proxy groups in the region, such as the Houthi rebels in Yemen and Hezbollah. In his address to the nation on Saturday night, Trump made reference to historical incidents the US believes the Iranians were responsible for over the years.

However, none of these actions is directly related to the strikes on Iran’s nuclear facilities.

What about a preemptive strike?

Another possible ground the US can use to mount a case for its bombardments is anticipatory or preemptive self-defense.

Both of these aspects of self-defense are controversial. They have never been clearly endorsed by the UN Security Council or the International Court of Justice.

The US has sought to assert a fairly wide-ranging, robust interpretation of the right of self-defense over many years, including both anticipatory self-defense and preemptive self-defense (which is particularly relevant in the Iran strikes).

The major point of distinction between the two is whether a potential attack is imminent. Anticipatory self-defense is in response to an attack on the brink of happening, such as when armed forces are massing on a border. Preemptive self-defense is a step further removed, before a genuine threat materializes.

Famously, in 2002, the administration of President George W Bush adopted what is known as the “Bush doctrine” following the September 11 terrorist attacks.

This doctrine was framed around the notion of preemptive self-defense justifying a strike on another nation. This was one of the grounds the US used to justify its military intervention of Iraq in 2003 – that Iraq’s alleged program of weapons of mass destruction posed an imminent threat to the US.

However, this justification was widely discredited when no evidence of these weapons was found.

Did Iran pose an imminent threat?

With regard to Iran’s nuclear program, an imminent threat would require two things: Iran having nuclear weapons capability, and an intent to use them.

On capability, there have been debates about Iran’s transparency with respect to its cooperation with the International Atomic Energy Agency (IAEA).

But, importantly, the IAEA is the body that has the authorization and capability to make judgments about a nation’s nuclear program. And it said, at this point in time, Iran did not yet have nuclear weapons capability.

As Rafael Grossi, the head of the IAEA told the BBC:

[…]whereas until the early 2000s there used to be […] a structured and systematic effort in the direction of a nuclear device, that is not the case now.

Trump’s statement in which he referred to the US military operation against Iran’s “nuclear enrichment facilities” was particularly striking. There was no reference to weapons. So, even the language coming out of the White House does not make reference to Iran possessing weapons at this point in time.

Further, many states have nuclear weapons capability, but they’re not necessarily showing intent to use them.

Iran has a long track record of aggressive rhetoric against Israel and the US. But the critical question here is whether this equates to an intent to strike.

What about collective defense?

Israel began its military campaign against Iran on June 13, also arguing for the need for anticipatory or preemptive self-defense to counter the threat posed by Iran’s nuclear program.

If Israel is exercising its right to self-defense consistently with the UN Charter, as it claims, it can legitimately call on the assistance of its allies to mount what is known as “collective self-defense” against an attack.

On all the available evidence, there’s no doubt the Israelis and Americans coordinated with respect to the US strikes on June 22. At face value, this is a case of collective self-defense.

But, importantly, this right is only valid under international law if the original Israeli right to self-defense is legitimate.

And here, we encounter the same legal difficulties as we do with the US claim of self-defense. Israel’s claim of an imminent attack from Iran is very dubious and contentious on the facts.

A concerning precedent

The overarching concern is these strikes can set a precedent. Other states can use this interpretation of the right of self-defense to launch anticipatory or preemptive strikes against other nations any time they want.

If this practice is allowed to go unchecked and is not subject to widespread condemnation, it can seen by the international community as an endorsement – that this type of conduct is legitimate.

There are many states acquiring conventional weapons that could be seen to pose a potential threat to their neighbors or other states. And there are several states considering the acquisition of nuclear weapons.

One example is Japan, where there has been some debate about nuclear weapons as a deterrence to future possible threats from China.

So, how might Japan’s actions be seen by its neighbors – namely China and North Korea? And how might these countries respond in light of the precedent that’s been set by the US and Israel?

Should Australia condemn the US strikes?

Australia’s Foreign Minister Penny Wong has come out in support for the US action, saying “we cannot allow Iran to have a nuclear weapon.” She hasn’t, however, addressed the legality of the US strikes.

The Albanese government should be discussing this. There’s an expectation, in particular, on the part of Labor governments, given former leader Doc Evatt’s role in the creation of the UN Charter, that they show strong support for the rules-based international order.

Labor governments were very critical of the way in which the Howard government engaged in the US-led invasion of Iraq, asserting there was no basis for it under international law.

Accordingly, there is an expectation that Labor governments should hold all states accountable for egregious breaches of international law. And, when viewed through the lens of international law, there’s no other way you can characterize the US strikes on Iran.

Donald Rothwell is professor of international law, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.