UNITED NATIONS, Aug. 16 (Xinhua) -- UN Secretary-General condemned Thursday the suicide attack a day before on an education center in the Afghan capital of Kabul that killed at least 48 students.

Guterres said in a statement through his spokesperson that those responsible for "this heinous attack" must be held accountable, noting many of the victims were students under the age of 18.

"The targeting of civilians, in particular children, is unacceptable," he said, conveying his sympathies to the government of Afghanistan and condolences to the families of the victims and wishing a swift recovery to the injured.

On Wednesday, the UN Security Council also condemned the attack, calling it a "heinous and cowardly terrorist attack."

In a press statement, the council reaffirmed that terrorism in all its forms and manifestations constitutes one of the most serious threats to international peace and security.

Earlier Wednesday, UN General Assembly President Miroslav Lajcak called the suicide attack "unacceptable," adding that the General Assembly continues to stand against terrorism and with Afghanistan.

He said many of the victims were young people preparing for university entrance exams, noting pursuing an education should not be risk to one's life.

Up to 48 students were killed and 67 others injured in a suicide bomb blast targeting a private education center in Dasht-e-Barchi of Kabul on Wednesday, the Afghan public health ministry said.

The UN mission in the country condemned the attack, saying in a statement that there is "no justification whatsoever for targeting civilians, at any time, under any circumstances."

No group has claimed responsibility yet. However, people pointed finger at the Islamic State group, saying the extremist outfit could be behind the deadly attack as it was in the past.