She hurled a grenade at a police checkpoint close to the scene of an earlier remote-controlled bombing in the city of Peshawar, a frequent target of al-Qaeda and Taliban fighters arrayed along the nearby Pakistan-Afghan border, before detonating her explosives.
Police officials said a second female suicide bomber was also killed in the blast before she could activate her vest.
"This was a female suicide bomber aged around 17 or 18 who threw a hand grenade on the police checkpost, 20 metres away from the site of the first blast, and then blew herself up," Shafqat Malik, a local police officer, told the AFP news agency.
"Her vest did not explode completely. She was killed and another woman was also killed and three policemen were injured." Terrorists are increasingly using women and children in school uniform in order to evade checkpoints in Pakistan's cities.
Four officers and a child were killed in the first explosion, when a bomb hidden in a handcart at the roadside tore through a passing police van carrying 20 constables about to start the day shift.
The bombings come a day after a US missile strike in the North Waziristan tribal region killed 21 militants believed linked to the Haqqani network, an al-Qaeda linked group fighting in Afghanistan.
The bombings come a day after a US missile strike in the North Waziristan tribal region killed 21 militants believed linked to the Haqqani network, an al-Qaeda linked group fighting in Afghanistan.