The Israeli military says it has expanded its ground operation against the militant Islamist Palestinian group Hamas to "every part" of the Gaza Strip.
The army resumed its offensive Friday after a weeklong cease-fire expired.
After focusing its ground operation on the northern part of Gaza in recent weeks, the military began carrying out airstrikes in southern Gaza as well.
The vast majority of Gaza's population has fled to the south in search of safety.
But late Sunday, Israeli military spokesman Daniel Hagari said ground troops were also pushing into the south.
"The Israeli army is continuing and expanding the ground operation against the Hamas presence in every part of the Gaza Strip," he said. "The forces are coming face-to-face with terrorists and killing them."
Earlier, eyewitnesses had told DPA news agency that Israeli ground troops had advanced into an area east of the city of Khan Yunis in the south of the Gaza Strip.
UNICEF calls for 'immediate humanitarian cease-fire'
The United Nations Children's Fund (UNICEF) said it was witnessing "massive child casualties."
UNICEF spokesperson James Elder was in southern Gaza and said the area was experiencing "the worst bombardment of the war right now."
"I feel like I'm almost failing in my ability to convey the endless killing of children here," he said in a video he posted on social media.
He called for an "immediate humanitarian cease-fire."
Israel reports 10,000 airstrikes on Gaza since war began
Israel's military says it has conducted around 10,000 airstrikes on targets in Gaza since the war began nearly two months ago.
The Israeli Defense Forces (IDF) said its targets included command centers, tunnels and weapons depots belonging to Palestinian terrorist organizations. The information could not be independently verified.
The announcement comes as international criticism of Israel's actions is growing.
Israel's aeriel bombardment has caused a large number of civilian casualties.
On Sunday, the Hamas-run Health Ministry said some 15,523 people have been killed in Gaza since the war erupted and another 41,316 have been injured.
According to UN estimates, around 80% of the 2.2 million inhabitants of the Gaza Strip have had to leave their homes because of the war.
ICC chief prosecutor wants to investigate all possible Gaza war crimes
The chief prosecutor of the International Criminal Court said his office will "further intensify its efforts to advance its investigations" of possible crimes by Hamas and Israeli forces.
Prosecutor Karim Khan said in a written statement issued after his first visit to the region that he witnessed "scenes of calculated cruelty" at the locations of the October 7 attacks.
During the visit, he spoke to family members of Israeli victims and called for the immediate and unconditional release of hostages taken by Hamas.
"The attacks against innocent Israeli civilians on 7 October represent some of the most serious international crimes that shock the conscience of humanity, crimes which the ICC was established to address," Khan said, adding that he and his prosecutors are working "to hold those responsible to account."
Khan also visited Palestinian officials in Ramallah, including President Mahmoud Abbas, and spoke to Palestinian victims.
He said of the war in Gaza that fighting in "densely populated areas where fighters are alleged to be unlawfully embedded in the civilian population is inherently complex, but international humanitarian law must still apply and the Israeli military knows the law that must be applied."
"We must show that the law is there, on the front lines, and that it is capable of protecting all," he added.
The Hague-based court has been investigating crimes in the Palestinian territories committed by both sides since 2021 but has yet to announce any charges.
Neither Israel or the US are member states of the court and do not recognize its jurisdiction.
Israel insists it is trying to safeguard Gaza civilians
Israel's government has rejected accusations that the Israeli military is doing too little to safeguard the civilian population in the Gaza Strip as it seeks to destroy Hamas.
"We will in parallel make the maximum effort to do two things: one — to differentiate between the terrorists who are our bitter enemy and the civilian population. We will do everything to safeguard that population," Israeli government adviser Mark Regev said on Sunday.
"We will facilitate the entrance into Gaza of humanitarian support for the civilians of Gaza," he added.
His comments come as international concern has been intensifying over the death toll in Gaza, which on Sunday reached more than 15,500, according to the Hamas-run Health Ministry.
Regev also said Hamas was exclusively to blame for the war in Gaza and for the resumption of hostilities following the cease-fire and was using residential areas, hospitals and mosques to hide its "military terror machine."
His comments were backed up by US National Security Council spokesman John Kirby who said the White House believes Israel is "making an effort" to minimize civilian deaths in Gaza.
"We believe they have been receptive to our messages here of trying to minimize civilian casualties," he told ABC's "This Week", including publishing an online a map of places where Gazans could go to find safety.
"There's not a whole lot of modern militaries that would do that... to telegraph their punches in that way. So they are making an effort."
Ron Dermer, Israel's minister of strategic affairs, insisted on ABC that efforts to minimize civilian casualties were deliberate and "unprecedented."
"If we wanted to do it fast," he said, "we'd harm a lot more civilians," he added.
Gazan Health Ministry: Death toll surpasses 15,500
The number of people killed in the Gaza Strip since the start of the war with Israel reached 15,523 on Sunday, the Hamas-run Health Ministry said.
Ministry spokesman Ashraf al-Qudra said 70% of those killed were women and children, while 41,316 people had been wounded.
A spokesman for the Hamas government press office said 700 people had been killed over the past 24 hours as fighting restarted after a weeklong truce.
Al-Qudra said only 316 dead and 664 wounded were removed from the rubble and taken to hospitals, but many others were still lying among the remains of buildings as emergency crews struggled to reach them.
Having initially targeted northern Gaza, Israel's military has urged Gaza residents to move out of specified areas in the south of the territory as it hit a wider area with aerial bombardments.
Israel's air and ground campaign is in response to an attack by Hamas militants on southern Israel on October 7 in which around 1,200 were killed and 240 taken hostage, according to Israeli authorities.
The militant Islamist group Hamas, which governs Gaza, is designated a terrorist organization by Israel, the US, Germany and others.
Israel says 800 tunnel shafts uncovered in Gaza
Israel's military says its soldiers have discovered 800 shafts leading to Hamas' network of tunnels below Gaza since October 27.
It added that more than half of them — around 500 shafts — had been destroyed using a variety of methods, including by "detonation and by sealing off."
It said many kilometers of tunnels had also been destroyed. It was not possible to independently verify the military's claims.
"The tunnel shafts were located in civilian areas, many of which were near or inside civilian buildings and structures, such as schools, kindergartens, mosques and playgrounds," the military said in a statement.
Before the current war broke out, Hamas, the Islamist Palestinian militant group that rules Gaza, said it had hundreds of kilometers of tunnels built into the territory's sandy soil.
Israel has sought to target the tunnels in its war with Hamas, for example with air strikes and army engineers using mapping robots.
Pope Francis urges new truce in Gaza
Pope Francis says he was saddened the seven-day truce in the war between Israel and Hamas had been broken.
"There is so much suffering in Gaza," the pontiff said, as he called on all parties to reach a new agreement to end the fighting as soon as possible.
He also said his thoughts were with the dozens of people still held hostage by the militants in Gaza, as well as the humanitarian situation of residents in the enclave.
The Palestinian territory lacks essential supplies, he noted, adding that the situation there was "serious."
The pope is currently suffering from lung inflammation. His words were read by an aide during his Sunday Angelus message.
