In a statement issued by the UN, Guterres said those behind the attack must be held accountable and brought to justice.
“The Secretary-General reiterates the urgency of achieving a peaceful settlement of the conflict. The United Nations remains committed to support the people and Government of Afghanistan in this important endeavour,” the statement added.
In a separate message on Twitter, the UN Assistance Mission in Afghanistan (UNAMA) expressed “outrage” at the killing of civilians.
“Extremists and spoilers need shunning,” the post read.
Saturday’s attack came as representatives of the Afghan government and Taliban are engaged in negotiations in Doha, Qatar, to end the conflict in the country which has raged for40 years, claiming thousands of lives and displacing millions of people.