On Saturday night, an IAF aircraft fired missiles at a Fatah training camp near Khan Younis in the Gaza Strip after spotting suspicious activity. Six Palestinians were killed in the strike. Weekend missile strikes killed a total of 14 Palestinians, including a seven-year-old boy. Security forces stepped-up their level of alert Sunday morning out of fear that Palestinian terror groups will launch attacks against Israel, either in retaliation for the weekend assault, or in preparation for Pessah. Troops and policemen beefed up patrols along the seam line with the West Bank as well as setting up roadblocks at the entrance to major cities and entertainment spots. A closure imposed on the territories last month will remain in place, officials said, at least until after Pesah in two weeks. The Shin Bet, over the weekend, recorded 75 terror alerts including 12 concrete threats to perpetrate anti-Israel terror attacks. Iyad Abu Aynayn, 29, a senior bombmaker affiliated with Hamas and the Popular Resistance Committees (PRC) in the Gaza Strip was killed Friday night together with his seven-year-old son and four other armed men in a missile strike on a PRC military training camp in the southern Gaza Strip. Aynayn's wife was seriously injured in the attack. On Saturday, IAF-launched missiles slammed into a car in Gaza City killing two members of a Kassam cell which the army said had just fired a rocket towards Israel. The pair - Mahmoud Ajour and Sami Abu Shariya - were identified as members of the Al Aqsa Martyrs' Brigades, a violent offshoot of Palestinian Authority Chairman Mahmoud Abbas' Fatah Party. A third member of the rocket squad was seriously wounded. But despite the targeted killings and escalation in the IDF's anti-Kassam operation launched a week-and-a-half ago and dubbed "Southern Arrow", Palestinian terror cells still succeeded in launching at least five rockets at Israel over the weekend. The IDF responded with artillery barrages that pounded Kassam launch sites in addition to IAF missile strikes on two access routes used by the rocket cells in the northern Gaza Strip. The actions drew a harsh response from the Hamas with Ghazi Hamad, a spokesman for the new government, calling the attack a brutal massacre. "Maybe it's an important message to the president (Abbas) today that Israel is not interested in peace or political compromises," he said. Nabil Abu Rudeina, spokesman for the PA chairman, called Friday's missile strike an "unforgivable crime," adding that "Israel's destructive policy is a continuing violation of the calm and will soon have painful consequences." Abu Rudeina called on the Quartet to intervene "in order to pressure Israel to stop its attack on the Palestinians." The heads of the Popular Resistance Committees in the Gaza Strip also issued threats and in a public message, said "the movement will not return to business as usual following the crimes committed by the Israelis. The movement's enemies will pay [and] the coming days will prove the seriousness of our intentions. The Zionist enemy must wait and see our powerful and painful response." In other developments, two Palestinians were killed when the tunnel they were crawling through under the Gaza-Egypt border collapsed, Palestinian police said. The tunnel apparently caved in overnight but the bodies were found only after dawn Saturday, the police said. The two Palestinians, police said, were from a family known for drug and food smuggling in the area. Meanwhile Saturday, IDF troops located an explosives laboratory in the Abu Sneinah neighborhood in Hebron. An explosion had rocked the laboratory on Friday night, apparently as a result of a work accident in which three Palestinians unintentionally detonated an explosive device that they were preparing to be used in an attack on IDF units operating in the city. The three Palestinians were wounded in the explosion and evacuated to a local hospital. Security forces found several pipe bombs and other explosive devices in the laboratory, which was blown up by Border Police sappers later in the morning.