The system's radar predicts the impact site of the missile as it lifts from Gaza and permits the operators to ignore those that will land in open areas, an important distinction since each interceptor costs US$50,000.
Eight people were wounded by rockets, only one seriously - a Thai farm worker hit in an open field.
Twenty-seven rockets heading for the cities of Beersheba, Ashkelon and Ashdod were intercepted.
Hamas, the major group in the Gaza Strip, refrained from participating in the missile firing and, according to Israeli spokesmen, asked Egypt to press Israel for a ceasefire. The rocket firing was carried out by al-Qassi's organisation, the Popular Resistance Committees, and by Islamic Jihad.
The man killed with al-Qassi, Ahmad al-Khanini, was among the Palestinian prisoners freed last year in exchange for captured Israeli soldier Gilad Shalit.
Israel's attack on al-Qassi, despite the near certainty that the Palestinians would retaliate with rockets, reflects the new situation prevailing after the overthrow of Egyptian President Hosni Mubarak last year.
Egyptian control of the Sinai Peninsula, which abuts Israel, has weakened and Palestinian militants from Gaza have established bases there, out of reach of Israel which will not attack them on Egyptian territory. Israeli officials say the pre-emptive attack on al-Qassi was intended to get to him before he reached Sinai.
The million Israelis living within a 40km range of Gaza were advised by civil defence authorities to sleep in shelters and reinforced security rooms, which have been attached to most apartments, and remain close to them during the day.
Schools were kept closed but workplaces functioned as usual.
The Iron Dome rocket-defence system, developed in Israel, became operational last year with two batteries and suffered technical problems in its early stages. There are now three batteries deployed around Gaza and a fourth is expected within a few months.additional reporting AP
