Said Siyam is the most senior leader of the Islamist militant organisation Hamas to have been killed since the beginning of the Israeli offensive on the Gaza Strip.
Hamas television said Mr Siyam, his son, brother Iyad and his brother’s family, had died when an Israeli missile struck his brother’s home in Gaza City on 15 January.
The Israeli military say he was killed in a joint operation carried out by the Israeli Southern Command and the Shin Beth internal security agency.
The 49-year-old was interior minister in the Hamas government and oversaw thousands of members of the Executive Force, a paramilitary organisation which played a key role in the group’s violent take-over of the coastal territory in June 2007.
He is also said to have been one of three members of the "collective leadership" of Hamas in Gaza since 2004, which was formed after Sheikh Ahmad Yassin and Abdel-Aziz Rantissi were killed by Israel.