The Pakistan Taliban said the attack was revenge against the Army for its crackdown in a tribal area. More than 130 children died in Tuesday's attack by gunmen on a school in Peshawar.
Tuesday's attack on a military-run school in Peshawar is Pakistan's bloodiest terror incident in several years. Last week saw a similar attack on a much smaller scale in Kabul.
Most of the dead are young students. Pakistani militants say they targeted the military-run institution in Peshawar in retaliation for military offensives in northwestern tribal areas.
A young Christian couple was accused of having desecrated a Quran on Tuesday and brutally murdered by a village crowd. Pakistan leader Nawaz Sharif vowed the attackers would be punished.
India said Pakistan was meddling in its internal affairs, but previous meetings haven't triggered diplomatic rows. Both countries claim sovereignty over Kashmir.