Hamas , Arabic acronym for the Islamic Resistance Movement, a Palestinian Islamic fundamentalist organization established in 1987 during the Intifada. An offshoot of the Muslim Brotherhood, Hamas operates mosques, schools, clinics, and social programs but is best known in the West for its military wing, which has carried out numerous terrorist attacks on Israelis. Hamas opposed the 1993 accord between Israel and the Palestine Liberation Organization (PLO), which granted Palestinians gradual limited autonomy in the Gaza Strip (see Gaza) and the West Bank and called for complete Israeli withdrawal from both areas. Since 1993 Hamas's military wing has carried out suicide bombings in Israel in an attempt to derail both that agreement and further negotiations. Hamas supporters have been prominent among those who have challenged the Palestinian National Authority, and its leaders have been subjected to mass arrests. The organization opposed the 1996 elections held in the Gaza Strip and the West Bank for the Palestinian National Authority but did not call for a boycott; some Hamas sympathizers ran as independents. In 2004, Israel killed Sheikh Ahmed Yassin, Hamas's spiritual leader, in retaliation for continued Hamas attacks.