"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.
A suicide bomber set off his explosives inside a mosque in the Afghan capital on Friday, officials said, killing at least 30.
In addition, 45 people were wounded in the attack, which took place during evening prayers inside the Imam Zaman Mosque in the city's Dasht-e-Barchi neighborhood, an enclave of ethnic Hazaras.
The bombings were the latest in a string of attacks this week that have killed an estimated 150 people in various Afghan provinces.
The Taliban claimed responsibility for the attack on their website, labelling the surge in suicide auto bombings and armed assaults as the "revenge of 750 bombs" in clear reference to 751 air raids conducted by the US forces against suspected militants in September alone. Residents say attendance at local Shiite mosques in Kabul on Friday has dropped by at least one-third.
Eyewitness Ali Mohammad said the mosque was packed with worshippers, both men and women praying at the height of the Muslim week.
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Around seven major attacks have been carried out in Afghanistan by Taliban or Islamic State group militants since Tuesday.
Afghanistan's minority Shi'ite population has been the target of several terror attacks this year that have been blamed on the Taliban and IS.
On Friday, 56 people were killed in a gun and suicide bomb attack at a Shia Muslim mosque, claimed by the Islamic State group.
No claim of responsibility has been made so far for the attack.
Afghanistan has seen a spate of suicide attacks and bombings in recent months.