Witnesses say Palestinian forces loyal to President Mahmoud Abbas have clashed with Hamas supporters despite a unity deal between the two rivals, AP reported.
The confrontation was the latest sign reconciliation efforts are in trouble.
Police broke up a Hamas rally in the West Bank late on Monday. Hassan Yousef, a Hamas leader, says officers stopped a convoy of 30 cars, seized Hamas banners and beat him and other protesters as well as journalists.
The Islamic militant Hamas seized the Gaza Strip in 2007, leaving Abbas only with parts of the West Bank. Last week's formation of a technocrat unity government was meant to end the split.
But tensions escalated and Hamas forced Gaza banks to stay closed for the past week amid a dispute with Abbas over salaries for its loyalists.