More than 200 Afghans killed in bloody week
"This afternoon when a minibus carrying army cadets was coming out of the military academy, a suicide bomber on foot targeted them, martyring 15 and wounding four," defence ministry spokesman Dawlat Waziri told AFP.
The attack takes this week's death toll from militant attacks to 200, and is the second major attack in Kabul in the past 24 hours.
At least 54 people were killed when a suicide bomber targeted a packed Shia mosque in the capital on Friday.
A Sunni mosque outside Kabul was also targeted during Friday prayers, killing at least 10 people.
No group immediately claimed responsibility for the attacks although the Islamic State group have targeted mosques several times in the country.
Abdul Hussain Hussainzada, a Shia community leader in Kabul, voiced concern on the new campaign against the minority group. "Our community is very worried," Hussainzada told AP.
Around seven major attacks have been carried out in Afghanistan by Taliban or Islamic State group militants since Tuesday.
The Taliban mostly hit security forces while IS have targeted Shia Afghans - whom the Sunni extremist group considers to be apostates - and civilian targets.
Earlier this year, following an attack claimed by the Islamic State group on the Iraqi embassy in Kabul.
The militant group effectively declared war on Afghanistan's Shia, saying they would be the target of future attacks.
Several mosques have been attacked following this warning, killing scores of Shia worshippers in Kabul and in western Herat province. Sunni mosques have also been targeted.
Residents say attendance at local Shia mosques in Kabul on Friday has dropped hugely due to fears of being targets.
The Taliban have taken responsibility for the earlier assaults this week that struck on security installations in the east and west of the country.
The US and NATO have poured more troops into the country, as Afghan security forces struggle to cope with the anti-government insurgency.
IS have managed to establish themselves in the country, hitting those deemed to be against their extremist ideology.
The Taliban have meanwhile managed to claw back control of much of the country with security forces infilitrated by the militias with army and police outposts regularly targeted.
Agencies contributed to this story.