CRS Reports & Analysis
Legal Sidebar
U.S. Strike on Syrian Airbase: Legal under
International Law?
04/17/2017
In his letter to Congress
under the War Powers Resolution, President Trump cited his Article II powers as his domestic
legal authority for the April 6 missile strike on Al Shayrat airbase in Syria, but did not describe a legal basis to justify
the action under international law. The missile strike may raise questions under international law including, in
particular, whether the action is consistent with U.S. obligations under the U.N. Charter. The answer may in turn raise
questions about whether the validity of the international legal basis has any bearing on the validity of the action pursuant
to U.S. domestic law. This Sidebar provides a brief overview.
Article 2(4) of the U.N. Charter prohibits the “threat or use of force against the territorial integrity or political
independence” of another Member state unless an exception exists. There are at least three sets of circumstances that do
– or may – constitute exceptions to this prohibition.
The first basis for an exception is U.N. Security Council authorization grounded in the powers granted to it by Chapter
VII of the U.N. Charter to respond to threats to international peace and security. That Chapter authorizes the Security
Council to “determine the existence of any threat to the peace, breach of the peace, or act of aggression” and to “make
recommendations and take other actions to maintain or restore international peace and security.” Express authorization
from the Security Council would provide the clearest legal basis for military action in response to Syria’s use of
chemical weapons. However, while the U.N. Security Council has adopted resolutions regarding the situation in Syria
(e.g., U.N.S.C. Resolution 2118, issued in 2013) that include language condemning the use of chemical weapons as a
breach of international law and a threat to international peace and security, the Security Council has stopped short of
authorizing the use of military force to enforce the prohibition.
The second basis for an exception to Article 2(4) limitations on the use of force is when such action is taken in self-
defense. Article 51 of the Charter explicitly recognizes the right of self-defense as an exception to Article 2(4)’s
prohibition. Specifically, Article 51 states, “Nothing in the present Charter shall impair the inherent right of individual
or collective self-defense if an armed attack occurs against a Member of the United Nations ....” There has been no
claim that Syria has conducted an armed attack against another nation. However, some theorists and practitioners,
consider that there also exists a customary doctrine of inherent self-defense outside of the circumstances identified by
Article 51. This doctrine would permit military action to counter a grave threat to regional peace and stability, even if
that threat seems to be contained within the borders of a state and there is no threat of imminent armed attack against
other states. Under this view, armed intervention to counter a valid threat is not a prohibited “use of force” under Article
2(4) so long as it is not aimed at taking a state’s territory or subjecting the state’s people to political control, and is not
otherwise inconsistent with the purpose of the U.N. Charter. Although the letter to Congress asserted that the missile
strike would “promote the stability of the region,” the Trump Administration has not claimed that the missile strike was
necessary to defend against the threat of an armed attack against the United States, its citizens, or its allies in the region.
Nor has the Administration to date informed the Security Council of measures taken in self-defense, as would be
required when acting under the terms of Article 51.
Third, some have argued that emerging norms of international human rights law provide that states are no longer free to
treat their people as they see fit under the guise of sovereignty, but are instead obligated to respect their people’s
