A member of Afghan security force stands guard at an attacked security checkpoint in Kabul, capital of Afghanistan, May 20, 2019. Three police officers were killed after unknown men hurled a hand grenade on a security checkpoint on Sunday in Dough Abad, an area in Police District 7 of Kabul. (Photos: Xinhua)

Afghan police officers inspect an attacked security checkpoint in Kabul, capital of Afghanistan, May 20, 2019. Three police officers were killed after unknown men hurled a hand grenade on a security checkpoint on Sunday in Dough Abad, an area in Police District 7 of Kabul.

Afghan police officers inspect an attacked security checkpoint in Kabul, capital of Afghanistan, May 20, 2019. Three police officers were killed after unknown men hurled a hand grenade on a security checkpoint on Sunday in Dough Abad, an area in Police District 7 of Kabul.

Photo taken on May 20, 2019 shows an attacked security checkpoint in Kabul, capital of Afghanistan. Three police officers were killed after unknown men hurled a hand grenade on a security checkpoint on Sunday in Dough Abad, an area in Police District 7 of Kabul.

A member of Afghan security force stands guard at an attacked security checkpoint in Kabul, capital of Afghanistan, May 20, 2019. Three police officers were killed after unknown men hurled a hand grenade on a security checkpoint on Sunday in Dough Abad, an area in Police District 7 of Kabul.