In 1915, the German paper “Der Arbeiter” published an article titled “The Austrian Red Book” where we can read a report of how the military and armed civilians of Serbia and Montenegro violated the Hague Regulations on the Practices and Customs of War on Land and the Geneva Convention by using prohibited ammunition. Serbo-Montenegrin troops also committed atrocities against the elderly, the sick, women, and children.

Cited from the article:

“The Austrian Red Book. Vienna, April 10.

A Red Book published today contains a collection of evidence of violations of international law by the states at war with Austria-Hungary.

In the introductory remarks of this collection, which falls apart in three lines, it is pointed out that the treatment and violation of the most primitive norms of the right of hospitality, sacred even among peoples of a lower level of culture, experienced by diplomatic and consular officials of Austria-Hungary by the authorities of enemy states is occurring on an unprecedented frequency. It must be described as particularly serious that the unlawful expulsion or arrest occurred several times even before the state of war had begun

Regarding the regime also largely applied before the start of the war against Austrian and Hungarian citizens in the enemy countries, the introductory remarks state: Even if one admits that it can be justified in certain respects if the enemy’s conscripted citizens are prevented from participating in the war, the methods applied by the authorities of the enemy states, especially the detention and imprisonment of the elderly, the sick, women, and children, contradict the most elementary duties of humanity.

A French legal scholar in particular found the words for such conduct: “To inflict harm on defenseless citizens of the enemy without the most compelling reason means a relapse into barbarism.”

The evidence cited for the infringements of martial law, which, however, represent only a negligible number compared to those that actually occurred, shows that there is hardly a norm of war law that enemy troops have not repeatedly violated. The numerous cases of the use of prohibited ammunition, the disregard of the Hague Regulations on the Practices and Customs of War on Land and the Geneva Convention, are followed by the fearsome atrocities of which the troops and population of Serbia and Montenegro are guilty.”

Reference

https://digital.tessmann.it/tessmannDigital/digitisedJournalsArchive/page/journal/62994/1/15.04.1915/357128/9/filterId-62994%01357128%014442767-query-Jugoslawische+Gr%C3%A4ueltaten-filterIssueDate-%5B06.10.1865+TO+06.10.1940%5D-filterF_type-Newspaper.html