VATICAN CITY (AP) — Pope Francis has exhorted Catholic bishops worldwide to do what's needed to ensure children aren't sexually abused by clergy.

The Vatican on Monday released the text of a Dec. 28 letter Francis sent to bishops about injustices to children such as slave labor, malnutrition and sexual exploitation, including abuse by priests.

In the letter, Francis decries the "sin of what happened, the sin of failing to help, the sin of covering up and denial, the sin of the abuse of power."

Francis tells bishops to "adhere, clearly and faithfully, to 'zero tolerance'" for sex abuse of minors.

The pontiff himself has been criticized by some for not punishing bishops who covered up abuse by reassigning molesters to different parishes.

Francis asks bishops for "complete commitment" so such "atrocities" won't re-occur.