NABLUS, West Bank, March 4 (Reuters) - Palestinian militants fired on a Palestinian police station on Friday in an incident that underscored difficulties new President Mahmoud Abbas faces in trying to impose law and order in the West Bank and Gaza.

The incident began when a member of the militant al-Awda Brigades, part of Abbas's Fatah faction, came to the station in the West Bank city of Nablus to visit his jailed brother, but was refused permission to see him by police.