An IDF helicopter fired a missile into the offices of a Palestinian terror organization in Gaza City overnight Saturday, Israel Radio reported. No further information was available on the attack. Earlier, air force jets struck at Kassam launch sites in three separate bombardments Saturday night. The Israeli attack came in retaliation for Kassam rocket attacks over the weekend which targeted the western Negev. Earlier on Saturday, Defense Minister Shaul Mofaz ordered the army to take immediate steps to intensify its response to the Kassam rocket attacks. Mofaz instructed the army to embark on a number of steps "from the ground and in the air," security sources said. In addition, indirect and direct messages were conveyed to the Palestinian Authority demanding it take immediate action to prevent further rocket attacks. A total of four Kassam rockets were fired at the western Negev. On Saturday night one rocket landed in the hothouses of Moshav Netiv Ha'asara. Earlier, two rockets landed in fields belonging to Kibbutz Karmia south of Ashkelon while, on Friday, a rocket landed in an open field of Kibbutz Nir Yitzhak. IDF artillery units deployed along the Gaza security fence retaliated by shelling open areas in northern Gaza where the rockets were launched. "The minister's instructions are in accordance with the ongoing policy to respond harshly to rocket and mortar fire," one of the sources said. Until now, Israel's response has been somewhat restrained, with artillery units deployed outside the Gaza Strip shelling open areas within Gaza identified as being the sites from which the rockets were launched. Violence within Gaza also escalated over the weekend with two Palestinians killed by the IDF in separate incidents, including one off the Gaza coast. Since the IDF pullout from the Gaza Strip, security officials have become concerned by increasing violence in the area. During that period, according to the army, security forces have intercepted and blown up 22 bombs placed by Palestinians for detonation near IDF units patrolling the Gaza security fence. There have been 170 mortar shell and Kassam rockets fired at the western Negev and eight confrontations with terrorists in addition to 75 Palestinian sniper attacks on troops. Before dawn on Saturday, a navy patrol boat sank a Palestinian fishing craft that had strayed into a restricted area off the Gaza coast. Ziad Dardawell, 22, was killed when the gunboat opened fire at the fishing vessel after calls to halt were ignored. During the incident, the patrol boat came under fire several times from light weapons from the Gaza shore and once from the fishing boat itself. Security officials believe that the fishing vessel was used to smuggle arms or terrorists into the Gaza Strip from Egypt. Palestinian media reports denied Israel's claims and declared that Dardawell was an innocent fisherman who had not strayed into a restricted area. The Palestinians also claimed that no warning shots were fired at the fishing vessel. According to an initial probe conducted by the navy on Saturday, the incident began shortly after midnight Friday when the navy spotted a number of Palestinian fishing craft heading towards Egypt. After the army notified Palestinian Police, the vessels were returned to Gaza and, after undergoing initial questioning by Israeli security officials, the fishermen were released. Shortly after, another Palestinian vessel was spotted heading for Egypt and, according to officials, one passenger was spotted in the craft. Three hours later it was spotted returning towards Gaza. The navy patrol boat then intercepted the fishing vessel and spotted two passengers on board. The patrol boat fired warning shots in the air, and called on the vessel to halt, but the calls were ignored. Shots were fired at the patrol boat from the Gaza coast, twice forcing it to go out to sea and out of the range of the gunfire. Each time the patrol boat returned and repeatedly fired warning shots at the fishing vessel. The third time, however, when warning shots were ignored, the navy patrol fired at the fishing vessel and identified hitting it but did not identify hitting anyone on board. The Palestinian Police were informed and later extricated one person from the boat. The navy patrol boat then shelled the fishing vessel, causing it to sink. It is not clear whether a second person spotted in the fishing vessel before it was hit succeeded in swimming to shore. In the coming days, the Palestinian Police will dive in the area to search for possible weapons the fishing vessel may have been carrying. On November 12, a 17-year-old Palestinian was critically wounded when a navy patrol opened fire at a fishing vessel after the Palestinians on board ignored calls to turn the vessel around. The army at the time said the boat had strayed 16 km. from the permitted fishing area. Late Friday night, Sayed Abu Lebda, 18, was killed and two others were wounded when soldiers opened fire at three Palestinians spotted climbing over the southern Gaza security fence in an attempt to enter Israel. Palestinian media reports later claimed that Lebda was mentally unstable. Hours earlier, soldiers arrested three unarmed Palestinians spotted as they attempted to cross the northern Gaza security fence into Israel. Earlier in the day, shots were fired at an IDF patrol north of the Kerem Shalom terminal crossing. In the West Bank on Friday, a Palestinian turned in a mortar shell and an RPG rocket to soldiers manning the Tarkumiya checkpoint outside of Hebron. That night, soldiers thwarted an attempt by four Palestinian youths to throw firebombs at Israeli vehicles on the Trans-Samaria Highway near Otzarin south of Nablus. The four fled when soldiers reached the site, leaving behind two firebombs ready for use.