At least six mortar shells were launched at IDF positions near the Gaza border Thursday, according to statements released by the military. No injuries or damage were reported in the two separate incidents.The IDF reported that soldiers stationed in the area came under mortar fire and returned fire on a Palestinian position shortly thereafter.Arab media claimed that the Palestinian mortar attacks were fired near a terror tunnel that was discovered earlier Thursday.After initially replying with tank fire, the Israeli Air Force attacked four targets in retaliation to the second round of mortar fire, which came a number of hours after the first barrage.The airstrikes targeted "terrorist networks belonging to the terrorist organization Hamas in southern Gaza Strip," a statement from the IDF Spokesperson's Unit said.The statement said the IDF will continue to act "with determination, and do whatever it takes to destroy Hamas's tunnels encroaching on Israeli territory."The incidents marked the third straight day in which Palestinians in Gaza fired at IDF soldiers on the border.Hamas launched a series of cross-border mortar attacks targeting IDF units on the border with northern and southern Gaza on Wednesday, prompting the IDF to return fire with tanks, and later air strikes on Hamas targets.The escalation - the most significant since the August 2014 cease-fire that ended a two-month conflict - came as Hamas sought to disrupt IDF work to detect its attack tunnels.On Tuesday, Hamas directed cross-border gun fire at an IDF engineering vehicle near southern Gaza.There were no injuries in this week's incidents.