KABUL: A suicide bomber killed 15 Afghan army trainees as they were leaving their base in Kabul on Saturday, the defence ministry said, in the latest deadly attack in the capital.

"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.

Kabul Crime Branch chief General Mohammad Salim Almas said police have launched an investigation into the attack which happened in the west of the city.

"The minibus was carrying army trainees to their homes from Marshal Fahim military academy," Almas told AFP.

There was no immediate claim of responsibility for the attack.

It was the second suicide bombing in the Afghan capital in 24 hours and the seventh major assault in Afghanistan since Tuesday, taking the total death toll to more than 200, with hundreds more wounded.

The spate of deadly attacks underscores deteriorating security across the war-torn country as the resurgent Taliban step up their attacks on police and military bases and Islamic State continue to target Shiite mosques.

It was the fifth time since Tuesday that militants have launched a major attack against Afghanistan's beleaguered security forces already badly demoralised by high casualties and desertions.

In the deadliest of the recent attacks, around 50 Afghan soldiers were killed in a Taliban-claimed assault on a military base in the southern province of Kandahar.

Insurgents blasted their way into the compound using two explosives-laden Humvees -- a tactic used in three separate attacks this week -- officials said.

The militants razed the base in the Chashmo area of Maiwand district to the ground, according to the defence ministry.

Afghan security forces have faced soaring casualties in their attempts to hold back the insurgents since NATO combat forces pulled out of the country at the end of 2014.