Gazans fired four Kassam rockets into Sderot on Saturday; one scored a direct hit on a home, sending several people into shock, on a day in which security forces killed six Palestinians in the West Bank and the Gaza Strip. IAF helicopters killed a member of a Kassam rocket cell in a car in the northern Gaza Strip on Saturday night, wounding one of his confederates. It was the second such missile strike since Israel accepted a Gaza cease-fire in November. Later in the evening, a Palestinian teenager was killed in Jenin when security forces raided her house in search of her brother, a wanted terrorist. Three terrorist organizations - Islamic Jihad, the Popular Resistance Committees and Fatah's Al-Aksa Martyrs Brigades - claimed responsibility for the rocket attacks in a joint statement. They said they were carried out to avenge the deaths of three terrorists killed by border police in Jenin earlier in the day. In the Jenin incident, an undercover Border Police unit killed three known terrorists belonging to the Aksa Martyrs Brigades who were driving in a car. Several hours earlier, gunfights broke out between troops and Palestinians in a village near Jenin. PA policeman Muhammad Said Abed, 22, was killed in the clashes. Separately, a full closure was imposed on the West Bank and the Gaza Strip starting at midnight, to remain in effect until after Independence Day on Monday. IDF officials said its liaison office would allow Palestinians to enter Israel in cases deemed "exceptional." AP contributed to this report.