U.N. humanitarian chief Stephen O'Brien says he saw "the early warnings of genocide" during a recent visit to Central African Republic, which has faced sectarian fighting since 2013.

He said in an interview Tuesday with The Associated Press that "there's a terrible development of militias now using ethnic or religious" reasons for attacks. He spoke with AP after briefing the U.N. Security Council on the trip behind closed doors at the request of France

During a visit to the southeastern town of Bangassou last month, O'Brien said, he saw 2,000 Muslims trapped in a Catholic church after fleeing their homes were burned by mostly Christian anti-Balaka militiamen who were "just lying in wait to kill them if they tried to move."

O'Brien said: "There's a very deep ethnic cleansing approach."