GAZA CITY, Gaza Strip — Israeli troops crossed into the Gaza Strip, killing eight Hamas militants in a fierce gunbattle Thursday that drew in Israeli aircraft, tanks and bulldozers.

Israel said its troops were on a routine foray against Palestinian Arab rocket squads when they came under fire from the militants about half a mile inside the Gaza Strip. Hamas said its fighters surprised an Israeli undercover unit.

Witnesses reported a heavy exchange of fire as Israeli tanks and bulldozers moved in, backed by air power.

As soldiers took up positions on rooftops, militants fought back by laying mines and firing small arms and mortars.

Two mortars landed on the Israeli side of the Erez crossing, which has been closed to most traffic since Hamas wrested control of Gaza last month, the army said. No one was hurt.

Hospital officials said six militants were killed in the clash. All belonged to Hamas, the group said, adding that the dead included its central Gaza field commander.

Two more Hamas militants were killed later Thursday in Israeli missile strikes targeting the same area, the army and hospital officials said. The fighting erupted near the Bureij refugee camp in central Gaza Strip, a site of frequent clashes between Palestinian Arab gunmen and the Israeli army.

Elsewhere along Gaza’s northern border with Israel, Hamas officials said some 15 tanks and three bulldozers had moved into Palestinian Arab farms and were leveling the land. The army said it had no such vehicles in the area.

Meanwhile in Gaza City, meanwhile, some 400 Fatah civil servants were prevented from entering their offices as part of the power struggle between the moderate Palestinian Arab government in the West Bank and the Hamas rulers of Gaza. The territories have been functioning as separate entities since Hamas seized Gaza by force last month.

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 Arab prime minister, recently announced the Palestinian Arab work week would run from Sunday through Thursday, as it does in Israel.

Hamas forces on Thursday barred people from entering government offices, saying they were closed because it was the official weekend. Most Palestinian Arab 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 its the official weekend. This is the beginning of the battle against the coup government in Gaza,” he said.

A Hamas security officer, Abu Dajana, said the orders of the “legitimate government” in Gaza would be implemented.

On Wednesday, Gaza government employees loyal to President Mahmoud Abbas of Fatah collected their first full salaries in 15 months. Civil servants who sided with Hamas’ bloody takeover of Gaza were not paid.