GAZA CITY, Gaza Strip — A Palestinian rights group says assailants have attacked a Catholic church in the Gaza Strip.The Palestinian Center for Human Rights says an explosive detonated in the church's yard. The group said an "abusive slogan" was written on the church wall. No further damage or injuries were reported.Hamas police spokesman Ayoub abu Shaar said Thursday an investigation was opened into the attack, which occurred Wednesday.Fewer than 3,000 Christians live among 1.7 million Muslim residents in Gaza. Their numbers rapidly have shrunk in recent years because of turmoil in the territory.In recent years, several Christian institutions were attacked by suspected Muslim hard-liners. In at least two cases, including the torching of a local YMCA, assailants were caught and sentenced to prison.