"The attack in Karachi is deeply saddening and utterly condemnable. Our thoughts are with the families of the deceased," he said.
"We stand firmly with the people of Pakistan in this hour of grief. I wish all those injured a quick recovery," the Prime Minister said.
At least 47 people from the minority Shia Ismaili community were killed and several others injured after eight gunmen entered their bus and opened indiscriminate fire in Karachi.
The gunmen stopped the packed bus, entered it and opened fire indiscriminately.