Islamabad - At least three police officers and one civilian were killed Friday in an explosion that targeted a security convoy in Pakistan's restive North-West Frontier Province (NWFP), officials said.

Eight people were also injured in the blast that occurred in Mardan, some 50 kilometres north-east of provincial capital Peshawar.

"It was a suicide attack," the district police chief Akhtar Ali Shah told Urdu-language Geo news channel. (dpa)