PESHAWAR: A woman covered in a head-to-foot burqa carried out a suicide bombing in northwestern Pakistan on Thursday, killing herself and another woman, police said, adding to security challenges confronting the U.S. ally.

The bombing occurred near a police check post just yards away from where a remote-controlled bomb hit a police van, killing four policemen and a child, less than an hour earlier.

The woman, said to be 25 years old, was wearing an explosive-laden vest and blew herself up in the heart of the main northwestern city of Peshawar.

"She exploded the vest as she came close to the check post. One policeman was wounded," police official Tariq Omar told Reuters.

He said a 60-year-old woman was also killed in the suicide bombing and police were investigating whether she was an accomplice or a passer-by.

Fourteen people were wounded in the earlier attack on the police van. The bomb, concealed in a push-cart, exploded as the van passed by.

Police said the attacks could have been coordinated.

Taliban militants have waged a campaign of suicide bombings across Pakistan, killing hundreds of people in recent years.

Female suicide bombing is rare in Pakistan, but any increase in the use of women for such attacks may complicate efforts by Pakistani security forces to stem the growing Islamist insurgency. Security officials are reluctant to search women in the conservative country.

In December, a burqa-clad bomber killed more than 40 people in an attack on a food distribution centre in Bajaur tribal region near the Afghan border.