At least 25 people, many believed to be students, were killed when a suicide blast ripped through a school in a Shia area of Kabul on Wednesday, officials said, the latest assault on Afghanistan's war-weary capital.
The attack on the Maw'ood education center in Dasht e Barchi area of the Afghan capital, came at 4 p.m. local time (7.30 a.m. ET), Kabul police spokesman Hashmat Stanikzai said.
Outrage was also growing on social media, where Afghans condemned the attack and angrily denounced those behind it - as well as the government for failing to protect them.
At least two gunmen were killed in the attack.
There was no immediate claim of responsibility for the attack.
"Children are not, and must never be the target of violence", said UNICEF's executive director Henrietta Fore.
In addition to the IS attacks, Taliban militants also delivered high-profile, demoralising blows in the strategic city of Ghazni - which they attacked last week, forcing security forces backed by USA air power to struggle for days to push them out - and in Faryab, where they captured a northern base, killing at least 17 soldiers.
Taliban spokesman Zabihullah Mujahid claimed responsibility for the assault.
The explosion, which came as the central city of Ghazni struggles to recover from five days of intense fighting between the Taliban and government forces, underlined how badly security in Afghanistan has degenerated, some two months before parliamentary elections scheduled for October. "They are killing our educated people and every day they are killing us".
At least 100 members of the security forces were killed in the fighting at Ghazni, officials have said.
Nahida Rahimi, a doctor at Kabul's Isteqlal Hospital, where some of the wounded are being treated, said a mother told her she had lost a son in Wednesday's bombing after already losing another a year earlier in another suicide bombing, also in Kabul, that targeted Shiites.
The United Nations Assistance Mission in Afghanistan called for the fighting to stop, saying up to 150 civilians are estimated to have been killed in Ghazni, where the public hospital was overwhelmed and water and electricity supplies cut.
Separately, six girls younger than 10 were killed when an unexploded mortar they picked up to play with suddenly exploded on Wednesday, officials in the eastern province of Laghman said. He said over 400 Taliban fighters took part.
Kandahar was the religious heartland of the Taliban during their five-year rule that ended with the 2001 invasion by USA and North Atlantic Treaty Organisation forces following the 9/11 attacks in the United States.