Israel hasbegun its ground operationin Gaza City, Israel Defense Forces Chief of the General Staff Lt. Gen. Eyal Zamir said Tuesday. "We are going to increase and enhance the strikes of our operation, and that is why we called you," Zamir said in Hebrew, addressing reservists who have been called up to serve in recent weeks. "We have already begun the ground operation in Gaza [City]." Israeli Prime Minister Benjamin Netanyahu also released a message addressing IDF reservists Tuesday. MORE: Gaza City could be destroyed if Hamas does not agree to terms to end war, Israel's defense minister says "I want to strengthen and express my deep appreciation to you, IDF soldiers and reserve soldiers and your families," Netanyahu said in the video message in Hebrew. "Now we are facing the decisive stage. I believe in you, I trust you and the entire nation embraces you." Netanyahu approved the military'splans to seize Gaza Citylast month. Last month, Israeli Defense Minister Israel Katz warned thatGaza City could "turn into Rafah and Beit Hanoun,"areas that were destroyed by Israeli strikes, unless Hamas agreed to Israel's terms for a ceasefire. "Soon, the gates of hell will open on the heads of Hamas' murderers and rapists in Gaza -- until they agree to Israel's conditions for ending the war, primarily the release of all hostages and their disarmament. If they do not agree -- Gaza, the capital of Hamas, will become Rafah and Beit Hanoun. Exactly as I promised -- so it will be," Katz said in a post on X. MORE: Pope calls for an end to violence in Gaza, supports churches that will not evacuate Israel's demands include the release of all hostages being held by Hamas, Hamas giving up control of governing the Gaza Strip and Hamas leaving the strip. In May, Israel accepted a U.S.-proposed 60-day truce that included the release of only some hostages, but Hamas rejected the proposal because it did not guarantee a permanent ceasefire, something Hamas has called for in several rounds of negotiations. Netanyahu has never agreed to fully withdraw Israeli troops from the strip, which has left negotiations stalled. On Tuesday, a senior adviser to Netanyahu told ABC News the Israeli government has outlined five principles they would need to see to end the war: the dismantling of Hamas' military and political capabilities; the immediate release of all hostages; the demilitarization of Gaza; Israel having "overriding security control" in Gaza for the "foreseeable future"; and the imposition of a civil authority in Gaza, which excludes Hamas and the Palestinian Authority. MORE: Israel begins attack on Gaza City, calling up to 60,000 reservists At least 76 people were killed and 281 were injured in the Gaza Strip in the last 24 hours, according to the Hamas-run Ministry of Health. Among those killed were 12 people trying to get humanitarian aid and another 90 were injured, according to the health ministry. Thirteen people, including three children, starved to death over the past 24 hours across Gaza, the ministry said Tuesday morning. Across Gaza, at least 361 people have died of malnutrition -- including 130 children -- since Oct. 7, 2023, the ministry said. During the month of August, there were a total of 185 malnutrition-related deaths among adults and children in Gaza, the health ministry said, calling it "the highest number in months." MORE: More than 100 aid groups warn of 'mass starvation' in Gaza amid Israel's war with Hamas The world's leading authority on food crises -- the IPC -- determined there was a famine less than two weeks ago. The IPC itself does not declare a famine, but its famine determination can be used by states and bodies such as the United Nations to declare a famine. Even before the famine determination was made,more than 100 aid groupsdescribed the dire food shortage in Gaza as "mass starvation," as the "Israeli government's siege starves the people of Gaza." The organizations warned that some aid workers are now joining food lines in Gaza, saying they are "risking being shot just to feed their families." Repeated deadly shootings around aid distribution centers have killed hundreds, according to the United Nations. ABC News' Tom Soufi Burridge contributed to this report. This is a developing story. Please check back for updates.