In the first deadly attacks since the start of Ramadan, a woman threw a hand grenade at a police checkpost, and then blew herself up, senior police official Shafqat Malik told AFP.

"Her vest did not explode completely. She was killed and another woman was also killed and three policemen were injured," Malik said.

"It is unclear whether the other woman was also an attacker or just a passer-by. Around eight kilograms of explosive material and ball bearings were used in the suicide vest," the police official said.

The explosion struck just meters from the site of an earlier attack that killed four policemen and a child in the Lahori Gate area of Peshawar.

"At least four policemen and a schoolchild have been killed in the attack," said Muhammad Faisal, a senior police official in the area.

He said that 18 other policemen are injured.

"The police van was carrying 20 policemen," said Imtiaz Shah, another police official, adding the vehicle was wrecked in the blast and a group of schoolboys were at the site when the bomb exploded.

"A 12-year-old boy has also been killed in the incident," he said.

Witness Mohabbat Khan, 45, told AFP that volunteers helped police evacuate the casualties after the attack.

"I was at home when I heard the blast. I came out and there were clouds of smoke. Then I saw the dead bodies and injured policemen. I shifted them to a police vehicle which reached at the site soon after the blast," he said.

Copyright AFP (Agence France-Presse), 2011