"Time has come for the federal government to take practical steps for the repatriation of the [Afghan] refugees," Mushtaq Ghani was quoted as saying by Afghan Khaama Press new agency after the decision was taken on Friday.
Ghani said that the Afghan refugees would be expelled in a month's time from the Khyber Pakhtunkhwa province, which borders Afghanistan to the northwest.
TTP militants said the attack had been made in retaliation for the recent advancement of Pakistan's armed forces against the extremist group in the northwest of Pakistan.
Meanwhile, the Afghan Taliban, alleged to support the Pakistani Taliban, condemned the school attack in an official statement, saying that the killing of innocent people, children and women was against Islamic law.
The Pakistani Taliban became active in 2007. The militant group is responsible for several deadly attacks in north-west Pakistan. The TTP aim to fight the Pakistani state and establish Sharia (Islamic) Law.