Three Kassam rockets were fired at southern Ashkelon on Tuesday evening. The rockets landed in a national park near the city's industrial zone, causing no casualties. Hamas claimed responsibility for the attack. Gaza sources said Israel carried out several air strikes overnight, but the army confirmed only one. On Tuesday evening, Palestinians said three civilians were lightly wounded in an IAF strike. Also Tuesday, the IDF killed nine Hamas operatives in joint ground and air operations in the Strip, amid a barrage of Kassam rockets on Sderot. Meanwhile, seven Hamas men were killed in an IAF strike on a Hamas military installation near Khan Yunis. The army said it was responding to Kassam rocket fire. On Tuesday morning, IDF troops shot and killed two Hamas gunmen in clashes along the Gaza border. Hamas's response was quick to come: By nightfall, more than 15 Kassam rockets pounded the western Negev, one of them scoring a direct hit on a home and a factory in Sderot and wounding three people. Meanwhile, with security services reporting an increase in motivation to carry out terror attacks following the bombing in Dimona, the Israel Police decided Tuesday to raise the national alert level to "C," the second-highest. Police said they would concentrate thousands of reinforcements around seam-line communities and in the South, as well as in the Jerusalem and Tel Aviv districts and in crowded areas. Security officials said Tuesday that the number of intelligence alerts have increased considerably since the attack, with over 50 warnings of different attempts to launch attacks against Israeli targets. Almost a dozen of those warnings were so-called "specific" alerts, pointing to particular targets or locales. In the 24 hours after the bombing, Border Police units throughout the country arrested 236 Palestinians who had illegally entered Israel to work. Two of them were wanted by the Shin Bet (Israel Security Agency) for questioning. Three stolen vehicles were also recovered in the operation. Terrorists often follow the tracks of these illegal workers in evading checkpoints and exiting the West Bank. The unfenced 30 kilometers of the southern edge of the West Bank is a popular crossing spot for workers from the Hebron area, and it is likely that this was the route taken by the Dimona bombers, who security forces believe already had some degree of familiarity with the Negev town. In previous months, Border Police operations in Dimona have discovered illegal Palestinian workers holed up in local building projects. Separately on Tuesday, Defense Minister Ehud Barak said Israel would defeat its enemies and that the IDF would succeed in stopping terrorism from the southern Hebron Hills, where security officials estimate the two Dimona bombers originated. "Just like your parents provided the solutions when they fought in the Jordan Valley, we... will now [find] solutions for the terrorism in Hebron and the Gaza Strip," Barak told cadets in the Officers' Course during an exercise at the Shizafon Base near Eilat. AP contributed to the report.