An Army of Islam gunman was killed Sunday in clashes with Hamas security forces in a Gaza City neighborhood, a Palestinian medical official said. A spokesman for the al-Qaida-affiliated group, identifying himself only by the nom de guerre Abu Hassan al-Makdesi, said that the clashes erupted as two of its members were arrested in a Hamas raid. Several people were wounded, including a Hamas man who was in a serious condition, Palestinians said. The confrontation came as Hamas launched a massive crackdown on Fatah supporters and institutions in the Gaza Strip following an explosion that killed six people, five of them members of Hamas's armed wing, Izzadin Kassam. By Sunday morning, some 200 Fatah men had reportedly been rounded up, while 40 Fatah-affiliated institutions were either raided or shut down. Islam Shahwan, a Hamas police spokesman, said his men seized "huge amounts" of explosives and weapons from Fatah in operations Saturday. He did not elaborate. Fatah forces responded Sunday by arresting 15 Hamas operatives, including two senior members of the group, in Tulkarm and 20 more in Jenin. A Fatah-affiliated group called Al-Awdah claimed responsibility for Saturday's explosion, but Fatah officials in Ramallah strongly denied responsibility and said the killings were part of a "settling of scores" among Hamas militiamen. Khaled Abu Toameh contributed to this report.