BBC NEWS | Middle East | Rival groups join forces in Gaza: "A major Palestinian security operation has begun in Gaza, in a joint effort by rival political parties to crack down on violence and lawlessness.
Hundreds of troops, some loyal to rival factions Hamas and Fatah, which only recently clashed in Gaza, have reportedly fanned out on the streets.
Up to 400 people have died in clashes since the Islamist Hamas won last year's parliamentary elections.
But the rival parties agreed to form a coalition government earlier this year."