Israeli helicopters fired three missiles early Thursday near Gaza City as about 50 tanks moved toward the town and the refugee camp next to it. One Palestinian was killed and three others were wounded, witnesses and hospital officials said.

Witnesses said gunmen went into the streets of Jabaliya, next to Gaza City, to confront the tanks, and there were exchanges of fire. A 60-year-old night watchman was killed and three other Palestinians were wounded, according to hospital officials.

The move came hours after a homicide bomber blew up a bus in the Israeli city of Haifa, killing at least 16. It was not clear if the Gaza operation was linked to the bombing.

Tanks surrounded the houses of two Hamas militants who were killed in earlier attacks on Israelis, the residents said. It appeared that the Israelis intended to destroy the houses.

In recent months, Israel has carried out a policy of destroying houses of militants as a deterrent measure. Palestinians complain that innocent relatives are made to suffer.

The Israeli military said its forces were carrying out an operation in Jabaliya refugee camp and confirmed that helicopters fired three missiles but gave no details of the target.

In the past, Israeli forces have targeted metal workshops where they say Palestinians make weapons, including mortars and rockets that are often fired at Gaza Jewish settlements and Israeli villages just outside Gaza.

Also, residents said that tanks were massing near the northern Gaza town of Beit Lahiya, next to Jabaliya.

Over the past three weeks, Israel has stepped up its military activity in Gaza, targeting Hamas, the Islamic group that took responsibility for blowing up an Israeli tank in northern Gaza on Feb. 15, killing four soldiers.