Israeli helicopters fired two missiles at a target south of Gaza City (search) early Wednesday, residents and Palestinian security officials said, and Israeli tanks moved into the city.

It was not immediately known what the target was or whether there were casualties.

Israeli military officials, speaking on condition of anonymity, said a "limited operation" was underway, involving the air force and tanks. The officials said the operation began with helicopters firing warning shots into an open area. They would not say what the object of the raid was.

Residents said after firing the missiles, the helicopters raked the area with machine gun fire, and Israeli tanks left the isolated Netzarim settlement nearby, entering Gaza City.

Witnesses said gunmen were exchanging fire with the Israelis, who entered the Ajlin neighborhood of the city.

Often during four years of fighting, Israeli helicopters have fired at suspected militants or at buildings where the Israelis say weapons are made, and forces have entered the city late at night to look for militants or weapons factories.

This was the first such operation since Mahmoud Abbas (search) won an election Sunday to succeed Yasser Arafat as head of the Palestinian Authority. On Tuesday, Israeli Prime Minister Ariel Sharon (search) telephoned Abbas to offer good wishes, and both sides said the two would meet, though no date has been set.

Despite the optimism, Palestinian militants in Gaza continue to fire mortars and homemade rockets at Jewish settlements and Israeli towns beyond the fence on a daily basis.