IDF tanks and aircraft fired at six targets in the Gaza Strip on Thursday after Palestinian Islamic Jihad fired a barrage of 12 mortar shells toward an army outpost.Calling the firing of the projectiles a “serious attack,” IDF Spokesman Brig.-Gen. Ronen Manelis said the projectiles were aimed at the IDF post and a cement factory on the northeastern edge of the Gaza Strip where construction crews are working on Israel’s new underground border barrier.The mortar fire set off alarms that were heard in Sderot and the Sha’ar Hanegev region.Train service in the area was temporarily halted and resumed an hour later, Israeli media reported. The IDF carried out two rounds of strikes near dusk.Tanks and aircraft hit two Hamas posts and two others that belonged to Islamic Jihad shortly after the barrage. Two additional strikes against PIJ posts were carried out by the IAF shortly afterward.There were no casualties and only minor damage to equipment following the firing of the projectiles. The Gaza Health Ministry said three people were lightly wounded by the Israeli strikes.Israel has begun building a state-of-the-art underground barrier that has a system of advanced sensor and monitoring devices to detect tunnels, combined with a six-meter- high aboveground smart fence. The fence, which will stretch along the entire Gaza border, including in the sea, is due to be completed by 2019.The mortar barrage is believed to have been PIJ’s response to the cross-border attack tunnel that was destroyed by the IDF on October 30, killing 14 terrorists.The group said the tunnel, which was detected using newly implemented advanced technology and destroyed in a controlled explosion inside Israeli territory, had been under construction “for years.”It vowed to take revenge for those who were killed.Following the incident, the IDF upped its alertness along the Gaza border and deployed Iron Dome batteries across the center of the country. “It is exactly one month since the IDF destroyed the tunnel, and Palestinian Islamic Jihad carried out their retaliation today,” Manelis said.Civilian communities were not threatened at any moment, and Israel has no intention of escalating the situation or initiating any hostilities on its southern border,” he said. “But any further action would be dependent on what happens in Gaza.”“We know exactly who fired the projectiles; we know their names,” Manelis said, adding that the IDF holds Hamas responsible for everything that occurs in the Hamas-run enclave.Islamic Jihad spokesman Daoud Shehab said Israel was trying to “cause confusion” and “divert attention away from the settlers’ crime in Kusra,” according to Palestine Today, a news website affiliated with the group.The Palestinian resistance has “the full right” to retaliate, he said.IDF Chief of Staff Lt.-Gen. Gadi Eisenkot and the head of the Southern Division and Intelligence met and decided that no further restrictions should be imposed on the civilian population of the region.Transportation and Intelligence Minister Israel Katz said Israel would continue to hold a “zero tolerance” policy toward enemy fire from Gaza.He said the mortar fire “proves that [Palestinian Authority President] Mahmoud Abbas is nothing more than a fig leaf that covers up a severe reality of armed and threatening terrorist organizations.”Jerusalem Post Staff contributed to this report.