The Israeli military said it had launched a ground operation within the Gaza Strip Thursday, in what it described as a defensive response to continued attacks from Islamist Hamas. The ground invasion began at night with Israeli attacks on several sides of Gaza — from the north, the east and the sea. Illumination flares were shot over Gaza City, the most densely populated part of the Gaza Strip and home to nearly 2 million Palestinians, to help Israel hit its targets. It is unclear how long the offensive will last. Israel urged Gaza residents to evacuate areas where the military is operating. Foreign journalists were also called on to evacuate coastline hotels. The operation is the first large-scale Israeli ground offensive in Gaza in more than five years. In tweets posted on its official account, Israel Defense Forces said the goal of the operation was "to target Hamas' tunnels that enable terrorists to infiltrate Israel and carry out attacks." It also said it had identified about 13 Palestinians who had infiltrated Israel through a tunnel dug from Gaza earlier Thursday. Israel had called up 48,000 reserve soldiers, and the military added that the government had approved the draft of an additional 18,000 reservists. "The IDF's objective as defined by the Israeli government is to establish a reality in which Israeli residents can live in safety and security without continues indiscriminate terror, while striking a significant blow to Hamas' terror infrastructure," a statement from the Israel Defense Forces read. The military said this course of action is meant to defend the state of Israel following 10 days of Hamas attacks and "repeated rejections of offers to deescalate the situation." The move also comes in the wake of the failure of Egyptian-led efforts to broker a cease-fire. “In the face of Hamas' tactics to leverage civilian casualties in pursuit of its terrorist goals, the IDF will continue in its unprecedented efforts to limit civilian harm," the statement read. In a phone conversation with Israeli Prime Minister Benjamin Netanyahu Thursday, Secretary of State John Kerry "emphasized the need to avoid further escalation and to restore the 2012 cease-fire as soon as possible," a statement from the U.S. State Department read. "The Secretary also reiterated our concern about the safety and security of civilians on both sides and the importance of doing everything possible to prevent civilian casualties," it added. Israeli soldiers had been massing on the border with Gaza in recent days and awaiting orders. Israeli strikes have hit more than 2,000 targets in Gaza and Hamas launched nearly 1,500 rockets at Israel, the Israeli military said, since July 8, when the recent confrontation between the two sides began. More than 200 people have died in Gaza during this time. Earlier Thursday, Gaza was rocked by another series of Israeli airstrikes and artillery fire hours after a temporary humanitarian truce came to an end. The attacks included an airstrike that killed three Palestinian children feeding pigeons on their roof. Rockets were also fired from Gaza into Israel and a Hamas-run television channel reported that Palestinian militants had successfully sent several armed drones over the border. The Associated Press contributed to this report.