The change, which also expands laws on genocide and war crimes, is part of a justice ministry bill expected to pass easily in parliament and come into force in July 2014, the Swedish press said.
Sweden's Minister of Justice, Beatrice Ask, told the daily Svenska Dagbladet that the current penal code required some improvements and "the way this kind of serious crime is dealt with will become much clearer".
Several people in Sweden have been sentenced since 2006 for war crimes committed during the Yugoslav wars.
In June this year the country's first trial for genocide concluded with a life sentence for the Swede of Rwandan origin, Stanislas Mbanenande.