, Jan. 24 (Xinhua) -- UN Secretary-General Antonio Guterres is "appalled and deeply saddened" by the attack on the offices of an international charity for children in , said the UN chief's spokesman in a statement on Wednesday.

Guterres expressed his deep sympathy to the families of the victims, said Stephane Dujarric.

Islamic State gunmen stormed the offices of Save the Children in the eastern Afghan city of Jalalabad on Wednesday, killing at least five people and wounding dozens of others.

"Humanitarian organizations provide life-saving assistance to the most vulnerable men, women and children in Afghanistan. Aid workers, and their premises and assets, should never be a target," said the statement.

The secretary-general reiterated that all parties to the conflict in Afghanistan are obliged under international law to protect humanitarian workers and civilians.