Unknown assailants set off two bombs early Friday in Gaza City, killing one man, Hamas security officials said. The first explosion took place just after midnight outside the Al Jazera cafe. The cafe has been hit twice in the past year by similar attacks, presumably perpetrated by radical Muslims who also target record shops and institutions they see as signs of Western influence. The powerful blast wounded three people and killed an unidentified man, the officials said. They spoke on condition of anonymity because they were not authorized to divulge details to the media. The second bomb exploded outside the house of a Hamas lawmaker, Marwan Abu Rass, not long afterward, causing light damage but no casualties, they said. The officials said police were investigating both blasts. AS well as clashes between the IDF and terrorists, Gaza has also been the scene of internal Palestinian violence, some of it carried out by fundamentalists who oppose what they see as signs of Western cultural encroachment. In recent years, shadowy groups have firebombed internet cafes, music stores and Christian institutions. The bombings are typically carried out late at night and most have caused no casualties. But in one deadly attack in October, 2007, a local Christian activist was murdered. No arrests have been made in the case. Meanwhile, Israel Radio reported Friday that Hamas security forces arrested an imam on Wednesday who had converted to Shia and preached in a Gaza mosque against the Hamas movement, saying its members were heretics. The imam was arrested along with several of his followers. A Hamas official denied the imam's arrest had anything to do with his sermons, and said he was detained for weapons possession and subsequently released.