How justified are the US strikes against the IRGC troops of Iran in Syria from the point of view of international law?

Question

Pentagon(U.S. Department of Defence 26 October 2023:

Today, at President Biden’s direction, U.S. military forces conducted self-defense strikes on two facilities in eastern Syria used by Iran’s Islamic Revolutionary Guard Corps (IRGC) and affiliated groups.

As I understand Iran officially supports to Syria in its fight against the IS terrorists.

But they have a conflict with the US, which are in Syria without official permission or a UN resolution.

Is there any more information why the US did this attack, and what is the legal status of such attacks in the UN Charter or ICJ cases?

And what does this mean?

...and mostly unsuccessful attacks against U.S. personnel in Iraq and Syria by Iranian-backed militia groups that began on October 17.

Are the Iranian-backed militia groups same as IRGC, and did the Iranian-backed militia groups attack the US bases, and then the US attack IRGC. Why?

Answer 1

Generally speaking in such incidents

On February 24 [2021], Mexico convened an informal meeting of the United Nations Security Council to discuss, among other things, whether the UN Charter permits the use of armed force by one State against non-state actors on the territory of another State without the latter’s consent. Twenty-four hours later, the United States did just that, carrying out airstrikes in Syria against several small facilities used by Iraqi militias. It is not alleged that Syria directed, controlled, or even supported these militias, so they are “non-State actors” for the purposes of this essay.

Were the airstrikes lawful? Unsurprisingly, the United States thinks so, while Syria and Iran think not. Most States won’t say. [...]

Brazil, China, Mexico, and Sri Lanka categorically rejected the use of force against non-State actors without the consent of the territorial State.

Austria took the intermediate position that it may be lawful to use force against a non-State actor if the territorial State is “unable, as a consequence of the complete absence of State authority and effective control over the respective territory, to prevent or suppress [the group’s] operations.” Notably, Belgium took a similar position in the past, but at the Feb 24 meeting stated that “States can have recourse to self-defense in case of attacks perpetrated by non-State actors … that are located on the territory of a sovereign State.”

Australia, Azerbaijan, Belgium, Denmark, Estonia, the Netherlands, Turkey, the United Kingdom, and the United States asserted a broad right to use force in self-defense against non-State actors in the territory of another State. [...]

Ambiguous Views: France, India, and Russia made statements that are hard to classify, though for different reasons. So did Norway, Pakistan, Qatar, and St. Vincent and the Grenadines. [...]

The remaining participants in the Feb 24 meeting either did not address the specific legal question (Armenia, Finland, Georgia, Iran, Ireland, Kenya, Liechtenstein, Ukraine) or said nothing from which their legal position can be reliably inferred (Ecuador, Peru, Syria, Tunisia, Vietnam).

So, depends whom you ask.

And TBH, the author of that piece (which declares himself on the "constrictive" side) is probably being too strict in classifying the positions of France, Russia, and India as "hard to classify". Those were all IMHO a "qualified yes", which added more conditions than the "expansive" views, but still allowed them in some circumstances.

Answer 2

Iran backed militias have claimed responsibility for previous attacks on US forces.

ISW Oct 26

The Islamic Resistance in Iraq—a coalition of Iranian-backed Iraqi militias—claimed three attacks on US military positions in Iraq and Syria. The group conducted one-way drone attacks on US positions at Ain al Asad airbase and Erbil International Airport on October 25 and 26.[34] The group also conducted a rocket attack on a US base near Hasakah in northeastern Syria on October 26.[35] The Islamic Resistance in Iraq has claimed 20 of the 22 reported attacks on US forces in the Middle East since October 18.

Regardless of the legal status of US forces in Syria in general - which does not form part of this Q - I rather doubt international law forbids a military force being fired upon from retaliating against the military opponent doing the firing. Or against another military unit affiliated with them.

It certainly does not seem problematic wrt Geneva Conventions for example.

Answer 3

In terms of UN charter, explicitly permitted:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Article 51.

Attacks occurred against United States assets. Until the UN takes measures (which it hasn't), the US retains rights to self defense.

The UN charter is explicitly clear here. It is permitted.

Answer 4

Q: why the US did this attack?

The US is retaliating because they want to stay there and that sends a message to all that we will do anything to prevent further attacks against US bases.

And give the message to Israel that we are doing our duty in the best possible way. See below for this:

Brett McGurk, the White House coordinator for the Middle East and North Africa, said the US had four main objectives in Syria: to reduce violence, maintain military pressure on ISIL, address Syria’s humanitarian crisis, and to support Israel.

.. mostly unsuccessful attacks

This line says that our casualties were few and don't worry. (Families, etc.) and the situation is under our control.

Are the Iranian-backed militia groups same as IRGC …

What do you mean by "same as"? Do you mean they are all IRGC troops? No. IRAN is very clear in this line. IRAN unlike the US (that is always looking for a way to quickly send more than 2000 troops to any country) teach them to fish instead of giving them fish. But of course there are always a handful of IRGC members to guide and direct them.

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NOTE: Maybe you don't know much about IRGC. it is normal among the western propaganda. IRAN has two type of armies. One official army that is for defending the country and another army/militia known as IRGC. The road and goal of IRGC is completely based on the holy book of Muslims. that is helping to the oppressed (Muslims) men, women, and children in the world not just in the country. [Quran ch 4- 75]

As you can see, IRGC is helping Iraq (after US invasion), Syria (after US and ISIS), Lebanon (after Israel invasion and ISIS), Yemen (after KSA invasion and ISIS), Bosnia (During Serbia attack) and Palestine (75 years of Israel occupation), all oppressed Muslim countries. (Of course, with the official permission of that country.)

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I want to add some important issues about illegal presence of US in Syria: Official:

Russia:

The unlawful US military presence in Syria is among the main destabilizing factors for the situation in the republic. "Washington's policy aimed at maintaining a de facto occupation of vast areas in the northeast of Syria, which are rich in oil, gas, and agricultural resources, as well as ongoing illegitimate sanctions pressure on Damascus leads to a further deterioration of the social and economic situation," Russian First Deputy Permanent Representative to the UN Dmitry Polyansky said.

Iran

The US troops’ presence in Syria is an occupation and an illegal act.

No action can be taken in Syria away from the opinion of its government and its people,

The U.S. must respond to the Syrian government’s demand to withdraw from its territory and stop plundering its resources.

China

China calls on the US to withdraw its troops from Syria and to stop plundering that country

Syria

The Syrian government has constantly expressed its opposition to the US role in Syria, and demanded US forces withdraw.

Syrian diplomats implored the international organization to put an end to what they view as violations of international law and the UN Charter by the US, which has stationed troops illegally in the northeast and southeast regions of Syria.

My Opinion: As the history of the United Nations and the United States shows, even if it were against all international laws, humanity, etc. (as Israel recently committed a war crime in a Gaza hospital and no one did anything), no one can do anything but World War III begins.