Afghan National Army (ANA) soldiers keep watch outside a military hospital in Kabul, Afghanistan March 8, 2017. [Photo/Agencies]

"This egregious and morally reprehensible attack targeted people at their most vulnerable, while they were receiving treatment in the hospital, and also targeted the medical staff caring for them," Pernille Kardel, the Secretary-General's deputy special representative for Afghanistan and acting head of UNAMA, was quoted in the statement.

"This cowardly attack reflects a fundamental rejection of the most basic principles of humanity," she said. "Without question, it amounts to an atrocity, and the perpetrators must be held accountable."

"Attacks on hospitals are a heinous crime against humanity and humanitarian law. No justification possible," the Afghanistan ICRC twitted.

"The attack on the Kabul military hospital is reprehensible and we condemn this attack in the strongest possible terms. Once again insurgents show complete disrespect for humanity by attacking a hospital. We stand with Afghan people against terrorism," NATO-led Resolute Support Mission said in a statement.

Several injured remained in critical conditions. And many women were among the victims.

The attack came as the country was marking the International Women's Day, which falls on March 8.

More than 3,490 civilians were killed and over 7,920 others injured in conflict-related incidents across Afghanistan last year, according to figures released by the UNAMA.