ISRAEL POUNDED HAMAS targets in Gaza with air strikes and tank shells Saturday, killing four militants, Palestinian officials said, as Palestinian missiles reached deeper into Israel in the most intense round of fighting since the Gaza war two years ago.

In all, 18 Gazans have been killed and more than 65 wounded since Israel unleashed the strikes following a Hamas attack on an Israeli school bus Thursday.

An anti-tank rocket struck the bus, seriously wounding a 16-year-old boy and injuring the driver.

After Israel’s devastating military offensive in the winter of 2008-2009, Gaza’s Hamas rulers had largely observed a cease-fire, and it was not immediately clear why the Islamic militants chose to end their relative restraint.

Israel, in turn, has pledged to strike back hard for the bus attack, in an attempt to restore the deterrence created by the Gaza war.

Violence has intensified in recent days.

Early Saturday, an Israeli airstrike struck a car near Rafah in southern Gaza, killing three Hamas militants. Later, Hamas said a tank shell killed another militant near the Jabalya neighborhood in Gaza.

Overall, the Palestinian death toll since Thursday includes 11 militants, a Hamas policeman and six civilians.

Hamas and Islamic Jihad fired more than 15 missiles into Israel Saturday. The rockets reached the vicinity of the Israeli cities of Ashdod, Ashkelon and Beersheba.

The military confirmed that its newly deployed Iron Dome defense system knocked some of them down. No Israelis were wounded in the attacks.

Reinforced rooms and early warning systems also have helped keep Israeli casualties low.

Hamas spokesman Sami Abu Zuhri said Saturday that the group’s attacks were still “limited and controlled” but that continued Israeli strikes may force it to escalate in response.

He said that Israel was trying to break the control of Hamas in Gaza.

Hamas has said the bus attack was in retaliation for the killing of three fighters in an airstrike earlier in the week.

It is not clear whether Hamas was trying to provoke a new conflagration with that attack, if it was not fully in control of all of its fighters, or if it believes Israel would pull back before invading Gaza again. Israel was condemned internationally after the Gaza war.

Thousands of rockets from Gaza have hit Israeli towns and cities since 2001.

Israel’s attempts to stop the rockets have included military incursions and covert operations abroad aimed at disrupting Hamas’ efforts to procure arms.

- AP