Islamabad, Pakistan (CNN) -- A teenage suicide bomber blew herself up Thursday at a police checkpoint in the northwest Pakistani city of Peshawar -- minutes after a blast targeting a police truck a few blocks away, authorities said.
The back-to-back explosions killed six people, in addition to the female bomber.
During the past few years, northwest Pakistan has been repeatedly hit by bombings but suicide attacks carried out by women are rare.
The first blast occurred when a truck carrying about 20 policeman passed by, said Hukam Khan, a senior official with the city's bomb disposal squad. The bomb was planted on a parked fruit cart and remotely detonated, he said.
The blast killed a child and four police officers, said Dr. Abdul Raheem, a senior medical officer of Lady Reading Hospital in Peshawar. It wounded 14 others.
Shortly afterward, the female suicide bomber first tossed a grenade at a police checkpoint -- then detonated her vest, said police official Shafqaat Malak.
The attack killed a passerby and wounded three others, police said.
Police said the casualties in the second blast were low because the attacker's suicide vest may have malfunctioned, setting off only a portion of her explosives.
Investigators say early indications are the suicide bomber was trying to get to the scene of the initial blast but was stopped at the checkpoint.
During the past few years, northwest Pakistan has been repeatedly hit by bombings but suicide attacks carried out by women are rare.
Peshawar is the capital of Pakistan's northwest province of Khyber Pakhtunkhwa, where insurgents have routinely targeted police and security forces.
In December 2010, a teenage female suicide bomber killed more than 40 people and injured more than 100 others at a food distribution point in Pakistan's tribal region.
No one immediately claimed responsibility for the attacks.
