GAZA CITY, Gaza Strip ? Israeli tanks today entered Gaza City and headed for a neighborhood where leaders of the violent Islamic militant group Hamas live, witnesses said.

A Palestinian policeman was killed and four civilians, including a doctor, were wounded by Israeli gunfire, hospital officials said.

It was the first time Israeli forces moved on the Sheikh Radwan neighborhood in northern Gaza City. The incursion came after Saturday’s blast in northern Gaza, in which four Israeli soldiers died when their tank set off a huge bomb. Hamas claimed responsibility.

Early today, witnesses said about 35 tanks, accompanied by attack helicopters, moved into position around a five-story building in Gaza City where Ahmed Ghandour and his family live and blew it up. Palestinians said Ghandour is the top aide to Hamas bombmaker Adnan al-Roul, believed responsible for planning the attack on the tank.

Two Palestinians were wounded slightly by Israeli gunfire, hospital officials said.

Israeli military sources, speaking on condition on anonymity, said an operation was under way in Gaza City but it was not a large-scale invasion.

Witnesses said that after surrounding the building, soldiers ordered everyone out and took the men away. Then soldiers sent dogs inside to see if anyone was left behind.

Israel has been blowing up the houses of suspected militants for several months as a deterrent measure. Palestinians and human rights groups charge that innocent relatives are made to suffer, but the Israelis believe that might give militants second thoughts about carrying out attacks.

After the tank bombing, Israeli leaders pledged to hit the Hamas infrastructure in Gaza.

Among the Hamas leaders who live in the Sheik Radwan neighborhood are Abdel Azziz Rantisi and Ismail Haniyeh, who often speak for the Islamic group. Spiritual leader Sheik Ahmed Yassin lives in another part of the city of 300,000 Palestinians.

On Sunday nine Palestinians were killed — six in a mysterious explosion in Gaza and three by Israeli army fire in the West Bank.

In Gaza City, a blast tore through the home of a member of the Islamic militant group Hamas, killing six Palestinians and wounding three, witnesses and hospital officials said. The six killed were Hamas members, the group said in a statement.

The cause of the blast was not immediately known. In the past, explosions have occurred when Palestinian militants mishandled bombs. A Hamas official said the explosion was in a car.