A female suicide bomber has targeted police at the scene of another bombing earlier Thursday in northwest Pakistan, with both blasts killing seven people.

In the first incident, a remote-controlled bomb exploded in a cart as a police vehicle drove by the Lahori area of the city of Peshawar. Five police officers and a child were killed in the explosion, which wounded more than 18 other people.

A short time later, a woman wearing a burqa approached the site of the roadside bombing. Police say the young woman threw a grenade before detonating her explosive-laden vest. Authorities say the vest did not fully detonate. The suicide bomber and another woman were killed in the blast, which wounded at least one police officer.

Police say they are investigating whether the second woman killed in the suicide bombing was an accomplice or a bystander. No group has claimed responsibility for the attack.

Attacks by female suicide bombers are rare but not unprecedented in Pakistan. In June, militants said they sent a married couple to carry out a suicide bombing at a police station in another northwestern town. That attack killed 10 people.

Peshawar, which lies near the country's restive border with Afghanistan, has experienced numerous suicide attacks and bomb explosions linked to Taliban and al-Qaida in recent years.