The IDF uncovered a Hamas attack tunnel stretching from southern Gaza into Israel on Thursday, as Hamas persisted in cross-border mortar attacks, sparking Israeli retaliatory strikes, and the security situation threatened to escalate further.Throughout the day on Thursday, Hamas fired mortars at IDF positions on four occasions, as it did on Wednesday, prompting tank and IAF air strikes on Hamas targets in Gaza. Palestinian sources said a woman was killed in one of the tank shell strikes on Thursday.On Thursday afternoon, the IAF launched its third wave of air strikes on Hamas targets in the space of 12 hours, in response to mortar fire.Two earlier waves of air strikes targeted Hamas targets in the early hours of the morning.Prime Minister Benjamin Netanyahu has called a special security cabinet meeting for Friday morning to discuss the recent escalation.Describing the process that led to the discovery of the tunnel on Thursday morning, a senior security source said, “We understood that we had located a tunnel. We are working in all areas, and have a number of focal points. In accordance with technological, operational, and intelligence efforts, we are improving all of the time. This has led us to focus in on certain areas, near the perimeter.”The source, describing the search process, added, “In places we understood that the focal points were incorrect, we left. In other areas, we thought we needed to continue. A number of hours ago, we found the tunnel.” The IDF estimates the tunnel to be around 30 meters deep underground.The IDF source said it did not know whether the tunnel was dug before 2014’s Operation Protective Edge or after it.The source said the tunnel is in “reasonable condition,” adding that sections of it may have been added after 2014. “We will investigate it and then destroy it,” he stated. “We view this technological, intelligence, and operational effort as a success. We can say that this tunnel is a violation of our sovereignty.”In the past 24 hours, Hamas understood that the IDF had begun approaching its tunnel, and wished to signal to Israel, through imprecise mortar fire, to stop, the source argued. “We are determined to continue with these efforts, and understand that we must focus in these areas. We are operating in the security perimeter, and not beyond,” he added.The IDF came under mortar fire from southern Gaza early Thursday morning, and three times in the afternoon and evening, prompting return tank fire.The IDF Spokesman added that the latest detection came after prolonged and widespread efforts led by the Southern Command and the Gaza Division.“IDF units are securing southern Gaza border communities,” the military said. “This tunnel was dug by the Hamas terrorist organization to carry out attacks in Israeli territory against Israeli civilians and security forces, and to harm Israeli sovereignty.”The Israel Air Force launched two waves of air strikes overnight between Wednesday and Thursday, striking a total of nine Hamas targets in the Strip. The IDF added that it had “the legitimate right and duty to ensure the security of civilians,” adding, “the quiet and routine life are a mutual interest [to both sides], and we will strive to upkeep them.” 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 Israeli injuries in this week’s incidents.“Terrorists who try to disrupt life in Israel will face severe retribution,” Defense Minister Moshe Ya’alon warned on Thursday night during a speech to mark Holocaust Remembrance Day, at Kibbutz Yad Mordechai near Gaza.“Today, too, those who seek our harm... should know that we will know how to place our hands on them, and they will not be immune, anywhere in the world. Terrorist elements should know... if they try to disrupt our lives, we will hit them hard,” he said.“We will not tolerate a return to a routine of fire and attempts to harm civilians and soldiers. We will act aggressively and with a steel hand, as we have done in the past 24 hours, against terrorist organizations in Gaza, Hamas chief among them, which is responsible for the fire [on us] and what occurs in Gaza,” Ya’alon added.Hamas’s military wing, the Izzadin Kassam Brigades, released a statement on Wednesday, saying, “We will not allow a continuation of Zionist aggression against the Gaza Strip. The enemy must not use any excuse, and it must leave the Gaza Strip immediately and deal with its fear and the fears of its residents outside of the buffer zone. The Zionist intrusions, since yesterday evening, constitute a clear breach of the 2014 agreement to reach calm, and a new aggression against the Strip.”On Tuesday, Prime Minister Benjamin Netanyahu visited the Gaza border with defense chiefs, saying that the past two years since the conclusion of Operation Protective Edge have been the quietest since Hamas took over the coastal enclave in 2007.In April, the IDF detected a deep Hamas attack tunnel stretching from the southern Gaza Strip into Israel. The discovery was kept under a media ban for several days. The tunnel was later demolished.