Ten Hamas militants died in clashes with Israeli forces Thursday, one of the deadliest days of fighting since the Islamic militant group wrested control of Gaza in mid-June, bringing the Israeli-Palestinian conflict back to center stage after months of infighting in the seaside strip.

Israel called in aircraft, tanks and bulldozers to press its military campaign against Gaza rocket squads, while militants laid mines and fired mortars at soldiers at a main Gaza-Israel passage. The conflict escalated quickly after a routine Israeli patrol just inside Gaza spotted armed militants approaching them and called in an airstrike.

After sweeping out its Fatah rivals in a lightning campaign last month, Hamas is trying to solidify its regime in Gaza, administering the crowded, chaotic, poverty-stricken territory. It 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.

The first 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 passenger crossing between Israel and Gaza.

Two of the mortars landed on the Israeli side of the passage, which has been closed to most traffic since Hamas wrested control of Gaza last month, the army said. No one was hurt, but the mortar shells ignited fire in a road at the crossing, the army said.

Hospital officials said eight militants were killed, and Hamas identified six as its members. The other two were not immediately identified. Among the dead was Mohammed Siam, 37, the Hamas field commander in central Gaza, Hamas TV said.

Israeli aircraft later fired missiles at targets in the area, the army said. Hospital officials said two militants were killed. Hamas said both were its members.

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

Hamas spokesman Abu Obeida said the group's fighters opened Thursday's clash by firing at an Israeli undercover unit. It set off the bloodiest day of conflict since June 27, when 12 Palestinians were killed in clashes with Israeli forces.

Deposed Palestinian Prime Minister Ismail Haniyeh of Hamas and a spokesman for the rival Fatah both condemned the Israeli operation and urged 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.

However, 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.

"We told them that the government in Ramallah announced new weekend days but they said the people in Ramallah are not the government," said Imad, 40, who works at the public works ministry, and refused to give his last name for fear of Hamas retribution.

"We are not coming on Saturday because it's the official weekend. This is the beginning of the battle against the coup government in Gaza," he said.

Abu Dajana, a Hamas security officer, said the orders of the "legitimate government" in Gaza would be implemented.

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.