The Ministry of Interior (MOI) said the blast happened close to the Sayeed-ul-Shuhada School in the Dasht-e-Barchi area on Saturday afternoon.
MOI spokesperson Tariq Arian said earlier the number of casualties could increase.
Officials have not revealed the cause of the explosion, or if there was a target. There has been no claim of responsibility yet.
Taliban spokesman Zabiullah Mojahid denied involvement in the explosion in a message to the media.
According to Afghanistan's Tolo News, the incident happened when students were leaving the school. "A car bomb blast happened first, and then two more explosions occurred near the girls school in Kabul," said Ibrahim, a schoolteacher, according to Tolo. He added that the majority of victims are girls, Tolo reports.
Afghanistan has seen a spate of car bombings over the last few months, despite peace talks being underway between negotiation teams of the insurgent Taliban and the government in the Qatari capital of Doha.
Violence in the country, at war for two decades, remains unacceptably high, foreign governments and institutions say, calling for an immediate ceasefire between the Afghan government and Taliban.
The National Intelligence Council assessed that the progress made over the last two decades "probably owes more to external pressure than domestic support, suggesting it would be at risk after coalition withdrawal, even without Taliban efforts to reverse it."
The two-page report, declassified at the request of Sen. Jeanne Shaheen, offers a grim assessment as fears mount about the potential degradation of hard-won women's rights in Afghanistan as US and NATO forces begin their withdrawal after nearly two decades on the ground.
Biden administration officials have warned that the Taliban would not achieve international legitimacy by seizing power by force or by limiting the rights of women.
In a CNN opinion piece published after Biden's withdrawal announcement, three women members of the Afghan government negotiating team warned that "if the Taliban does not believe the United States is firmly committed to a stable and democratic Afghanistan, that could spell trouble for our future talks."