Armed conflicts claimed at least 95,000 lives last year, with most of those killed being civilians, Swiss researchers said.
The deadliest conflict was in Syria, where an estimated 55,000 people died, according to the first annual War Report published on Tuesday by the Geneva Academy of International Humanitarian Law and Human Rights.
A total of 7,500 people died in Afghanistan, but an even larger death toll - 9,000 - was registered in Mexico, where criminal organisations are fighting both the army and each other.
The study found that a total of 24 countries were involved in international or internal armed conflicts. This figure includes the occupations of Cyprus and the Palestinian Territories.
Conflicts resulted in very few war crimes prosecutions or convictions in 2012, although the report noted that Britain and the United States had prosecuted some of their soldiers in Afghanistan.
