An Israeli warplane dropped a 2,000-pound bomb on the home of one of Hamas' top five decision-makers Thursday, instantly killing him and 18 others.

The airstrike on Nizar Rayan was the first that succeeded in killing a member of Hamas' highest echelon since Israel began its offensive Saturday. The 49-year-old professor of Islamic law was known for personally participating in clashes with Israeli forces and for sending one of his sons on a 2001 suicide mission that killed two Israelis.

Eighteen other people, including all four of Rayan's wives and nine of his 12 children, also were killed, Palestinian health officials said.

Israel has targeted Hamas leaders many times in the past, and the current leadership went into hiding at the start of the offensive. Rayan, however, was known for openly defying Israel and in the past had led crowds to the homes of wanted Hamas figures — as if daring Israel to strike and risk the lives of civilians.

More than 400 Gazans had been killed and some 1,700 wounded since Israel embarked on its aerial campaign, Gaza health officials said. The United Nations has said the death toll includes more than 60 civilians, 34 of them children.

Since Saturday, three Israeli civilians and one soldier have also died in rocket attacks that have reached deeper into Israel than ever before, bringing more than a tenth of Israel's population of 7 million within rocket range.