A new IDF protocol for defending Israel from Kassam attacks dictates that IAF planes will aerially monitor Gaza Strip districts from which Kassam rockets are most frequently launched and open fire if suspicious activity is spotted. The protocol has not, however, been implemented and still requires more specific delineation of the areas to monitored so as to not harm innocent civilians, Army Radio reported. Despite the mandate to refrain from harming civilians, potential air force targets will be populated areas, and not open territory, as have seen the thrust of much of the recent IDF response to Kassam and mortar fire. The IDF said that it would notify civilians in targeted areas a number of hours prior to carrying out the missions. On Thursday, Israel threatened to launch a ground operation in Gaza after five soldiers were wounded when a Kassam rocket fired from the Gaza Strip landed in an IDF base near Ashkelon. "Certainly if the rocket fire on Ashkelon does not stop, there will be a very fierce response, and no option can be ruled out, including a ground operation," Vice Premier Ehud Olmert told Channel 1, adding: "But of course we must conclude that this is the right method at the time we make the decision." The Prime Minister's Office, however, played down the possibility of a ground invasion of Gaza, threatening only to respond harshly to any further rocket attacks. "Until now, the rockets have been terrorist acts, but now they constitute an act of war," said Ra'anan Gissin, a senior adviser to Prime Minister Ariel Sharon, "and we will react with commensurate severity." Two Kassam rockets fired on Thursday landed near Ashkelon. The first rocket landed near an industrial zone, while the other struck the Yiftach army base and lightly wounded five soldiers, including a battalion commander. Four of the wounded were taken to Ashkelon's Barzilai Hospital, and the fifth to Soroka Hospital in Beersheba. The Islamic Jihad claimed responsibility for the attacks. Earlier in the week, another rocket landed in the IDF basic training base of Zikim, but there were no casualties. In both cases, the IDF returned fire with an artillery barrage on the Palestinian launch sites, a military policy that began in late September, with the advent of Operation First Rain, and has continued ever since. Gissin said that a new operation would aim to create an "intolerable situation" for the population in Gaza to pressure the Palestinian Authority into clamping down on cross-border attacks. He did not elaborate. However, a senior military source said that, barring a conquest of Gaza or taking "very drastic measures," the IDF was doing all it could against the Kassam threat. "One-hundred and fifty-nine Kassams have been fired since disengagement," said the source. "Over half of those have fallen in Palestinian territory." He noted that the reason why the rockets fell short was because Palestinian artillery crews have been afraid to get too close to the Gaza border fence. The IDF has killed 35 terrorists in the northern part of the Strip since September. "For every kilogram of explosive that falls on Israeli territory, a ton falls on Palestinian territory," said the officer. The Associated Press reported that a 21-year-old Palestinian man, Ibrahim Naana, was hit by shrapnel from Thursday's retaliatory artillery barrage, though it is unclear whether Naana was a civilian or combatant. In the West Bank on Thursday, the IDF said troops killed three terrorists in Nablus. According to the Palestinian Center for Human Rights (PCHR), soldiers laid siege early Thursday morning to a four-story building in the Rafidya neighborhood and shot three wanted men to death. They were Bashar Hanani, 29, who was the head of the Popular Front for the Liberation of Palestine infrastructure in Nablus, and two members of the Fatah-affiliated Aksa Martyrs Brigades - Ahmed Abdul Ra'ouf Khaled al-Jayousi, 22, and Anes Ahmed Mahmoud al-Sheikh Hamad, also 22. Military sources said that Hanani was allegedly responsible for planning the suicide bombing in the Carmel Market in Tel Aviv on November 1, 2004 which killed three civilians and wounded over 40. The IDF said he was also behind numerous attacks against Israeli targets. These included: An attempt to detonate a 25 kg. explosive device against IDF troops in Nablus in conjunction with a shooting attack. The attack was thwarted following the arrest of Palestinian university students, who had been recruited by Hanani to carry out the attack. An attempt to carry out a suicide bombing, which was thwarted following the arrest of many of the operatives involved and the subsequent disclosure of the location of an explosive bag which would have been used to carry out the attack. An attempt to carry out a suicide bombing at the Na'alin military base, which was thwarted following the arrest of the members of the terror cell which Hanani had recruited to carry out the attack. The same cell had also been planning to kidnap soldiers. An attempt to activate an explosive device against soldiers at an IDF base near Nablus. Activation of a car bomb against IDF troops in Nablus, in which no one was injured. In the past few months, Hanani had been planning additional attacks, including a suicide bombing inside Israel as well as the detonation of a powerful explosive device against Israeli targets, the army said. In addition, Hanani was responsible for a large number of shooting attacks against IDF troops in Nablus. Also Thursday, Atef Dawoud Hassan, 38, who managed the Dawa charity affiliated with the Islamic Jihad, was arrested in the village of Kfar Atira, north of Ramallah. Hassan allegedly funneled money to the families of jailed terrorists and suicide bombers through Dawa. Another Islamic Jihad member was nabbed in Hebron. In addition, the Samaria military court indicted Muhammad Kashua, 25, from the West Bank village of Ilaar on Thursday for transporting a suicide bomber to the open-air market in Hadera on October 26. The attack, committed by the Islamic Jihad, left six dead and another 27 wounded.