Palestinian militants have attacked a police station in the West Bank town of Nablus, sparking a gunfight with Palestinian police.

Witnesses say several militants took up positions outside the police station Friday and began shooting, prompting police to return fire. At least two people were reported wounded.

The gunmen were from a small militant group al-Adwa, affiliated with Palestinian Authority President Mahmoud Abbas' Fatah faction.

There are conflicting reports as to what the gunmen were upset about. One report says a militant was refused permission to visit his jailed brother, while another quotes police as saying the group was upset that one of its members had been beaten while in police custody.

Friday's incident underscores the challenges facing Mr. Abbas as he tries to rein in militants and restore law and order.