Is there a difference between providing defensive vs. offensive weapons to Ukraine when it comes to international neutrality laws? Not really. At least, according to a recent report by the Congressional Research Service entitled International Neutrality Law and U.S. Military Assistance to Ukraine. The United States, the European Union (EU), and other nations have supplied many forms of security assistance to Ukraine since the Russian invasion in February 2022. Many of these weapons have been defensive in nature – anti-aircraft missiles, anti-tank missiles, body armor, helmets, and medical supplies.
The provision of more ‘offensive weapons’ such as tanks, armored personnel vehicles, and assault helicopters has taken place in recent weeks. This, despite strident warnings by Russia and the threats of a nuclear response. Russia is accusing the United States and other nations of being belligerents to the conflict.
International neutrality law defines a country not taking part in an international armed conflict as a neutral state and one engaged in a conflict as a belligerent. The international agreements that were drafted over 100 years ago state the neutral states cannot provide ammunition or war material of any kind to belligerents.
Scholars are describing the traditional law of neutrality as one that does not work well in the new age of warfare. Some countries have adopted the doctrine of qualified neutrality; where states can take non-neutral acts when supporting the victim of an unlawful war of aggression (such as the Russian invasion of Ukraine). 20th century developments have overtaken some aspects of the law of neutrality. The United Nations charter weighs in on this issue – and lends justification to the concept of qualified neutrality. Modern international law, according to some scholars, allow for an intermediate position in which countries can actively assist victims of unlawful wars.
Neutrality law does not distinguish between defensive and offensive weapons. In any event the qualified neutrality doctrine would seem to give the United States the ability to provide defensive and offensive weapons to Ukraine without being classified as a belligerent. The Congressional Research Service report cited above explains this in greater detail.
International Neutrality Law and U.S. Military Assistance to Ukraine, CRS, April 26, 2022, PDF, 5 pages.