"Most of the victims were the displaced people from the Orakzai agency where the military has launched an offensive recently, displacing a large number of people.
"The attack is said to have involved a suicide bomber and perhaps a remote-controlled device planted near that particular area."
But he said there is no clear indication as to who is responsible for the attack.
"The first explosion prompted people to come to the assistance of the victims, at which point the second explosion took place, which shows that this was well planned [and] meticulous."
The Pakistani military stepped up an offensive against Taliban-allied fighters in Orakzai late last month.
The UN said earlier this month that the deteriorating security situation in Orakzai and neighbouring Kurram district has forced 200,000 civilians to flee since November last year.
Over the past year, Pakistan has significantly increased operations against fighters in its northwest and tribal belt which the US has branded an al-Qaeda "headquarters".
The area became a stronghold for hundreds of fighters who fled neighbouring Afghanistan after the US-led invasion in late 2001.
Much of the violence in Pakistan has been concentrated in the northwest of the country.
On Friday, at least eight people were killed and another 35 wounded in a suicide bomb attack at a hospital in Quetta, the capital of Balochistan.
A television cameraman and a police officer were among those killed when the attacker detonated his explosives outside the gate of the Civic Hospital's emergency ward.
Family members of a bank manager, who had been shot dead in the early hours of the morning, had gathered outside the hospital before the blast occurred.
The emergency room was full of his friends and relatives when the bomber struck at the gate, Mohammad Sabir, a police official, said.