Reactions from around the world followed a Pakistani Taliban attack on a military-run school in Peshawar which killed more than 130 people, most of them children.
UN Secretary-General Ban Ki-moon described the the attack as "an act of horror and rank cowardice."
U.S. President Barack Obama has condemned what he called a "heinous attack" on the Pakistani school.
The White House said in a statement that Obama reiterated support for the Pakistani government's efforts "to combat extremism and terrorism."
U.S. Secretary of State John Kerry said in London the attack "angers and shakes the world," and called for the perpetrators to be brought to justice.
President Ashraf Ghani of neighboring Afghanistan said in a statement "The killing of innocent children is contrary to Islam."
French President Francois Hollande condemned what he described as a "vile" attack, and pledged support for Pakistan's government in the fight "against terrorism."
Foreign Minister Frank-Walter Steinmeier said Germany condemned the attack "in the sharpest possible terms."
Nobel Peace Prize winner Malala Yousafzai, a native of Pakistan, said she was "heartbroken by what she called a "senseless and cold-blooded act of terror."
David Griffiths, Amnesty International's Deputy Director for Asia-Pacific, said, "There can be absolutely no justification for targeting children in this way."
Meanwhile, Pakistani Prime Minister Nawaz Sharif on December 16 vowed to continue an ongoing anti-Taliban operation in the region "until the terrorism is rooted out."