The Taliban has claimed responsibility for the attack on a police academy near Kabul, that left dozens of recruits dead, Al Jazeera reported.
The bombing left at least 27 dead, and another 40 injured in the suicide bombing, government officials told reporters on Thursday.
District governor of Paghman Mousa Rahmati told reporters that the attack took place around 20km west of Kabul.
He said the trainee police officers were returning from a training centre in Wardak province and were heading to the capital on leave.
The Taliban said it was behind the attack.
Former Afghan parliamentarian Daoud Sultanzoy said the death toll in the "very well coordinated and pre-planned" attack was expected to go up.
"This attacker and the group had enough information to conduct this atrocity in a well-planned manner," he told Al Jazeera, adding that the recent increase in attacks was a sign of Taliban desperation.
"The Taliban, we should expect that they will increase their attacks because they're suffering in the war front, their commanders are being killed, their activities are being hampered in a very major way by our security forces."
The attack is the latest major assault by the group and comes just nine days after 14 Nepali security guards killed in a suicide bomb attack on their minibus, also in the city.