Earlier reports had put the casualty at 28 civilians, one police officer and three attackers after the deadly Monday explosion and ensuing gun firing that rocked the office near a diplomatic district, according to a spokesman of the Ministry of Interior Affairs.
Around 20 people, including three policemen, were critically wounded, at least 10 of whom have later succumbed, spokesman Najib Danish said in a brief message to the media.
Hundreds of employees were trapped inside the building at the time - and some reportedly jumped to safety. The Afghan Special Operations Forces managed to rescue over 350 people, he added.
The attackers used a suicide bomber to detonate a car bomb outside the office, which provides service to family members of soldiers and ordinary people who lost their lives during the war or terrorist attacks.
Then at least two gunmen made their way inside the building, spraying bullets on the people inside before security forces' arrival, Xinhua news agency reported.
The attack occurred in Makruyan-e-Awal locality near Shashdarak, where several foreign embassies are located. The area also gives home to several apartment buildings and several government offices, including Afghan Ministry of Public Works.
It was not yet clear who carried out the attack, as none have claimed responsibility. Both Daesh and Taleban have carried similar attacks in the past.
The violence comes after a tumultuous few days for Afghanistan's political stability. Last week it was reported that the US planned to drastically reduce its military presence in the country, shortly after President Donald Trump announced an entire withdrawal from Syria, the BBC said.
On Sunday, Afghan President Ashraf Ghani replaced his defence and interior ministers with hard-line opponents of the Taleban who used to work for the country's intelligence agency.
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