Two schoolboys were killed and their brother injured on Wednesday when a bomb exploded in a Pakistan village playground near the Afghan border, officials said.
The trio, all brothers, were playing when the explosive device went off in Nisarabad village on the outskirts of Khar, the main town in the Bajaur tribal region, local administration chief, Adalat Khan, told AFP.
Two of them, aged between nine and 11 years, were killed and their 13-year-old brother wounded, he said. They were school students, he said.
A security official confirmed the casualties, saying that it was unclear if the bomb was planted by militants or was left during a six-month battle fought between government forces and Islamist insurgents.
Hundreds of people were killed in the fighting which saw heavy artillery and helicopter gunships pound Bajaur, to purge the area of militants.
The fighting ended in February when the military claimed to have "secured" the area.
Pakistan's semi-autonomous northwest tribal belt has become a stronghold for hundreds of extremists who fled Afghanistan after the US-led invasion toppled the hardline Taliban regime in neighbouring Afghanistan in late 2001.
Meanwhile, two people were killed in a bomb blast on Wednesday in the southwestern city of Quetta, the capital of the oil and gas rich Baluchistan province, bordering Iran and Afghanistan, police said.
"At least two passers-by were killed and four others injured when an improvised explosive device planted on a motorbike went off on the outskirts of Quetta," local police official Asad Nasir told AFP.
He said that the motorbike was parked near checkpost of the paramilitary Frontier Corps (FC), adding that no one had claimed responsibility for the attack.
Hundreds of people have died in an insurgency which flared in late 2004 in Baluchistan, where rebels are demanding political autonomy and a greater share of profits from the region's natural resources.