(Adds Hamas commander killed)

GAZA, Sept 20 (Reuters) - Israeli soldiers killed four Palestinians in the Gaza Strip during an incursion on Thursday, hospital officials said, one day after the Jewish state declared the Hamas-controlled territory an "enemy entity".

Gunmen confronted the Israeli force and set off explosives, and an Israeli helicopter also took part in the clashes in Bureij refugee camp in the central Gaza Strip.

A local Hamas commander, who Hamas said had been the target of the Israeli incursion, was killed by troops who had surrounded his house.

A senior Hamas operative, a 22-year-old militant and a 16-year-old civilian were also killed, medical workers said.

An Israeli military spokesman in Tel Aviv said an Israeli force shot a gunman during "activity against terrorist infrastructure" in the Gaza Strip.

Israel pulled soldiers and settlers out of Gaza in 2005 but has continued to carry out raids into the territory to try to curb cross-border rocket attacks by Palestinian militants.

Israel declared Gaza an "enemy entity" on Wednesday and said it would reduce its fuel and power supplies.

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