Satyarthi, who received the Nobel Peace Prize a week back along with Pakistan's Malala Yousafzai, who was also the target of a Taliban attack, said Pakistan government must take all possible steps to protect children and schools from violence.
"If they can hear me, they can keep me hostage, kill me but release those 400 children of mine who are trapped there," he said.
In a series of tweets, Satyarthji expressed his anguish and urged all right-thinking people to rise against the "inhuman" crime.
"My heart bleeds for bereaved families. One of the darkest days of humanity," he said adding "these are all our children who've been murdered today. My prayers and condolences are with the families.
"Pakistan government must take all possible steps to protect children and schools from violence. Children are the first casualty of violence and war. It is time we all came together and put a stop to this violence," Satyarthi said.