"We all know the principle: each State has the primary responsibility to protect its own people. However, when states require assistance, the international community must be ready to help", he said in a message to a seminar on "A Framework for Genocide Prevention".

Ban is in Cancun, Mexico, to attend the high-level segment of the UN climate change conference.

"And when States manifestly fail to protect their populations, the international community must be ready to take action", he said.

Ban emphasized the need to first understand the causes and dynamics of genocide in order to prevent the scourge.

"We need to understand what kinds of environments may encourage genocide, and which structural and operational factors can leave a population vulnerable or, alternatively, help to protect it", he added.