IDF fired artillery at open spaces in northern Gaza, as a preliminary response to the Kassam rocket salvo that hit Sderot Tuesday evening. Palestinian officials said no one was hurt. Meanwhile, Defense Minister Amir Peretz convened an emergency meeting with IDF officials to weigh further action in retaliation for the salvo. Chief of General Staff Lt. -Gen Gabi Ashkenazi was also present in the meeting. Earlier, Hamas said its men fired the Kassams. It was the first time in three weeks that Hamas has taken responsibility for a rocket attack. Hamas officials said the salvo was retaliation for Israel's killing a militant during an attack near a border crossing earlier Tuesday and also to commemorate the May 15 founding of Israel in 1948, known to Palestinians as al-Naqba, or "the catastrophe." Yaakov Katz and AP contributed to this report.