"Indiscriminate attacks against civilians are grave violations of human rights and international humanitarian law and can never be justified. Those responsible for today's attack must be brought to justice," said the statement released in Addis Ababa, where the UN chief is attending an African Union summit.
The secretary-general extended his deepest condolences to the families of the victims and wished a speedy recovery to those injured. He expressed his solidarity with the government and people of Afghanistan, Xinhua reported.

A suicide bombing has killed at least 102 people and injured at least 158 others in central Kabul, officials said.
The attack, claimed by the Taliban, was the deadliest for months. It followed a Taliban attack on a luxury hotel in Kabul a week ago that killed 22 people.