The U.N. peacekeeping mission in South Sudan (UNMISS) Tuesday voiced grave concern over mounting evidence of gross human rights abuses in the strife-torn country, including extra-judicial killings of civilians and captured soldiers, massive displacements, and arbitrary detentions, often on ethnic grounds. "I condemn in the strongest possible terms the atrocities committed against innocent civilians of different communities by elements from both sides during the crisis," U.N. Secretary-General Ban Ki-moon's special representative and head of UNMISS, Hilde Johnson, said. "There is no excuse for these terrible acts of violence. All perpetrators must be held accountable."