A four-year-old boy was killed and two other children injured due to a blast in Quetta's Killi Barat area on Monday, police said.

The three children were playing in the street when unidentified assailants lobbed a grenade near them, police official Izzat Ali said.

The boy succumbed to his injuries on the way to Civil Hospital Quetta, Ali said, adding that the two girls, approximately three-years-old each, were injured in the attack.

The nature of the blast and motive behind it are yet to be ascertained, Ali said.

Police reached the spot and cordoned off the area as an investigation into the attack went underway.

The Bomb Disposal Squad was called in to conduct a sweep of the area and confirm the nature of the blast soon after the incident.