Violent clashes between rival Palestinian factions in the Gaza Strip have left up to 10 people wounded.
The clashes on Friday erupted within 48 hours of Palestinian security forces having begun deployment in Gaza under a new security plan.
Hamas said the fighting began before dawn when members of the national security forces loyal to Mahmoud Abbas, the president, detained a member of Hamas's armed wing.
The man was detained because he was suspected of being involved in firing on security forces overnight, according to a source with the national security forces.
Hamas fighters responded by storming the facility where the man was being held and freeing him. At least two members of the national security forces were injured, one seriously, in the gun fight.
The security deployment started late on Wednesday, with forces setting up checkpoints and taking up positions at main intersections and government buildings.
"The new government should show signs of maturity and responsibility"
Husky, Ottawa, Canada
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The increased presence of security began shortly after Abbas and Ismail Haniya, the prime minister, agreed to finalise the security plan details and hold intensive talks starting on Thursday with security chiefs to agree on implementation mechanisms.
On the streets in Gaza, residents welcomed the security forces, hoping that it would end the lawlessness.
Public demand for the restoration of law and order had reached a new peak after incidents of armed robbery, kidnapping, and bombings reached an all-time high while security forces seemed unable to contain the lawlessness and violence.