"The government of India strongly condemns this barbaric crime against humanity.
"Our prayers are with the families and loved ones of all those who lost their lives or were injured in this barbaric incident. We hope the almighty gives them the courage and fortitude to bear their irreparable loss.
"There never has been, nor will there ever be, a justification for terrorism," the ministry statement added.
External Affairs Minister Sushma Swaraj cancelled a dinner she was to host Tuesday night for parliamentarians.
Child rights activist and Nobel laureate Kailash Satyarthi said: "My heart bleeds for bereaved families. It is one of the darkest days of humanity. The Pakistan government must take all possible steps to protect children and schools from violence."