Israel said its forces fought Hamas gunmen inside the militants' vast tunnel network beneath the besieged Palestinian enclave of Gaza, seeking to free hostages and to push forward its campaign to wipe out the militant group.
As the battle inside Gaza intensified, Israeli prime minister Benjamin Netanyahu dismissed calls for a halt to the fighting.
But international aid officials warned that a public health catastrophe was engulfing civilians in Gaza, with hospitals struggling to cope with the casualties and food, medicine, drinking water, and fuel running short.
Medics in Gaza's Indonesian Hospital said they had to set up an operating room in a corridor because the main surgical theaters were full from a sudden influx of civilian casualties from Israeli bombing early on Tuesday.
The tunnels under the cramped enclave are a prime objective for Israel as it expands its ground operations and pushes further into Gaza from the north to hit Hamas in retaliation for the Islamist group's deadly surprise attack on southern Israel three weeks ago.
Some of the 240 hostages that Israel says were seized by Hamas that day are believed to be held in the tunnel complex, adding a further complication for the Israelis on top of the difficulties of fighting in an urban setting.
"Over the last day, combined IDF [Israel Defense Forces] struck approximately 300 targets, including anti-tank missile and rocket launch posts below shafts, as well as military compounds inside underground tunnels belonging to the Hamas terrorist organization," the Israeli military said in a statement.
Militants responded with anti-tank missiles and machine gun fire, it said. A number of militants were killed, it said, without specifying a number.
Israeli forces also bombed Gaza overnight in air, sea, and ground attacks, hitting northwestern areas of the enclave, which Hamas rules, witnesses said on Tuesday.
On Monday, Israeli forces had targeted Gaza's main north-south road and attacked Gaza City from two directions.
Gaza health authorities say that 8,525 people, including 3,542 children, have been killed in Israeli attacks since Oct. 7. U.N. officials say more than 1.4 million of Gaza's civilian population of about 2.3 million have been made homeless.
About 1,400 people were killed in the Hamas assault on Oct. 7, Israel says.
Reuters has been unable to independently verify casualty counts.
The al-Qassam Brigades, Hamas's armed wing, said militants clashed early on Tuesday with Israeli forces invading southern Gaza. Four vehicles were targeted with missiles, it said.
The militants also fired at two Israeli tanks and bulldozers in northwest Gaza, al-Qassam said. In Beit Hanoun, in the northeast, they "liquidated" an Israeli unit which was ambushed as it entered a building.
Reuters was unable to confirm the details of the reports on the fighting. The Israeli military had no immediate comment on the Hamas accounts.
Air raid sirens sounded in the area of Israel's Red Sea city of Eilat on Tuesday and the Israeli military said it downed an approaching "aerial target."
There was no immediate claim of responsibility. Last week, Israel accused the Iran-aligned Houthi movement in Yemen of sending drones that caused explosions in two Egyptian towns on the Red Sea, saying they were intended to strike Israel.
The mounting death toll in Gaza has drawn calls from the United States, Israel's main ally, other countries, and the U.N. for a pause in fighting to allow in more humanitarian aid.
Israel has blockaded the Gaza Strip and refuses to allow in fuel supplies, saying they could be used by Hamas for military purposes.
Netanyahu said on Monday that Israel would not agree to a cessation of hostilities and would press ahead with its plans to wipe out Hamas.
"Calls for a ceasefire are calls for Israel to surrender to Hamas, to surrender to terrorism, to surrender to barbarism. That will not happen," Netanyahu said in televised remarks.
(Reporting by Nidal al-Mughrabi, Yomna Ehab, Ali Swafta, James Mackenzie, Henriette Chacar, Dan Williams, Emma Farge, and Jonathan Landay; writing by Steven Coates and Nick Macfie; editing by Simon Cameron-Moore and Angus MacSwan)