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Zimbabwe
Practice Relating to Rule 14. Proportionality in Attack
Section A. General
Zimbabwe’s Geneva Conventions Act (1981), as amended in 1996, punishes “any person, whatever his nationality, who, whether in or outside Zimbabwe, commits any such grave breach of … [the 1977 Additional Protocol I]”. 
Zimbabwe, Geneva Conventions Act, 1981, as amended in 1996, Section 3(1).
In its oral pleadings before the ICJ in the Nuclear Weapons case in 1995, Zimbabwe fully shared the analysis of other States that “the threat or use of nuclear weapons violates the principles of humanitarian law prohibiting the use of weapons or methods of warfare that … are disproportionate”. 
Zimbabwe, Oral pleadings before the ICJ, Nuclear Weapons case, 15 November 1995, Verbatim Record CR 95/35, p. 27.
The Report on the Practice of Zimbabwe considers that the principle of proportionality is a norm of customary international law but states that its application is difficult to gauge under war conditions. 
Report on the Practice of Zimbabwe, 1998, Chapter 1.5.