Israel moved quickly to bolster its security after the failed attempt on Sheikh Yassin's life.

Hamas has threatened "unprecedented revenge" for Israel's military operation against its revered founder, who is 67 and confined to a wheelchair.

The Israeli Government imposed a closure on the West Bank and Gaza Strip and denied Palestinians entry to the Jewish State for work.

Security forces also increased their presence in shopping malls, central bus stations, and other public areas that could be targets of suicide bombings by Hamas.

Sheikh Yassin and 15 others were slightly wounded when an F-16 jet-fighter dropped a 250-kilogram bomb on a residential building Saturday in Gaza City.

Senior Israeli military officers claimed that Sheik Yassin and other Hamas leaders were meeting at the time to plan new terror attacks.

It is understood that among those at the meeting were Hamas's top bomb-maker, Mohammed Deif, who heads Israel's most wanted list of Palestinian fugitives.

A senior Israeli police official said that in light of the failed attempt on Sheikh Yassin's life, the question was not whether there would be a Hamas terror attack, but when and where.

Israeli Prime Minister Ariel Sharon says efforts to hunt down and kill Hamas leaders will continue unabated. He says they are now "marked for death."

His warning is in line with previous statements made following the Hamas suicide bombing of a bus in Jerusalem three weeks ago that killed 22 Israelis.