Israeli forces pulled out of the Gaza Strip early Friday after a fierce military incursion that left 11 Palestinian militants dead and pushed Gaza's rival factions together in urging their people to fight back.

Israel sent infantry, tanks and bulldozers into Gaza on Thursday while militants laid mines and fired mortars at soldiers at the Erez passenger crossing between Israel and Gaza.

The raid, the latest in a series of similar operations aimed at Palestinian rocket squads and militant groups in the chaotic coastal territory, came as the Islamic group Hamas worked to solidify its regime after sweeping out its Fatah rivals in a lightning campaign last month.

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Hamas has initiated few attacks against Israel, but also has not stopped other groups from firing rockets at Israeli towns almost daily — provoking Israeli military action and drawing Hamas forces in.

Fighting escalated quickly Thursday after an Israeli patrol just inside Gaza spotted armed militants approaching and called in an airstrike. That clash erupted close to the Bureij refugee camp in the central Gaza Strip, a site of frequent clashes between gunmen and the Israeli army.

Witnesses reported a heavy exchange of fire as Israeli tanks and bulldozers moved in and soldiers took positions on rooftops. Hamas and Islamic Jihad militants hit back with small-arms fire, laid mines in front of the soldiers and fired mortars at the Erez crossing between Israel and Gaza.

The army said two mortar shells hit on the Israeli side of the passage, which has been closed to most traffic since Hamas seized Gaza. No one was hurt, but the explosions ignited a fire in a road, the army said.

Nine militants were killed in clashes in and around the Bureij refugee camp in central Gaza, hospital officials said. Hamas identified six as its fighters, while three remained unidentified. Among the dead was Mohammed Siam, 37, the Hamas field commander in central Gaza, Hamas TV said.

Later in the day, missiles launched by Israeli aircraft killed two more Hamas men, the group said.

Israel frequently sends forces a short distance into Gaza, where they look for tunnels that might be used for infiltrations or attacks. Armored bulldozers are also used in border areas to flatten land used by militants to launch their short-range homemade rockets.

A spokesman for Fatah joined Ismail Haniyeh, the deposed Palestinian prime minister who now heads the Hamas regime in Gaza, in condemning the Israeli operation and urging Palestinians to fight back.

"We assert that our people have the full right to defend themselves and to confront these aggressions," Haniyeh said, and Fatah official Hazem Abu Shanab echoed his thoughts.

But the two rivals squabbled on another front Thursday, when about 400 Fatah civil servants were prevented from entering their Gaza offices in an argument over the official weekend.

The Hamas-dictated work week in Gaza runs from Saturday to Wednesday, with Thursday and Friday assigned as the weekend. Salam Fayyad, the new Palestinian prime minister, recently announced the Palestinian work week would run from Sunday through Thursday.

Hamas forces on Thursday barred people from entering government offices, saying they were closed because it was the official weekend. Most Palestinian civil servants are loyal to Fatah.

On Wednesday, Gaza government employees loyal to Fatah collected their first full salaries in 15 months, but civil servants who sided with the bloody Hamas takeover of Gaza were not paid.

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