A previously unknown group apparently affiliated with Fatah claimed responsibility Tuesday for the bombing of a car of a Hamas activist and four other blasts that have targeted the Islamic group since its violent takeover of the Gaza Strip. The bombings were a new tactic in Fatah-Hamas tensions in the Gaza Strip since rivalry between the two groups erupted into five days of street warfare in June. An explosion went off before dawn Tuesday in the car of Hamas activist Said Dahshan in Gaza City, injuring no one but causing serious damage to the vehicle parked outside his house and to the building itself, Hamas said. A statement claiming for Tuesday's blast and four others in the past week - which also caused no casualties - was posted on the independent Gaza-based Ramattan news Web site later in the day. The bombings were retaliation for "Hamas crimes," the statement said, without elaborating. It was signed "The Brigades of Martyrs of Security Agencies" apparently in reference to members of the Fatah-affiliated security forces who were killed when Hamas wrested control of Gaza.