Israel says its forces attacked Hamas gunmen inside the Islamists' vast tunnel network beneath Gaza, after Prime Minister Benjamin Netanyahu dismissed calls for a halt to fighting to ease humanitarian crisis.
The tunnels are a key objective for Israel as it expands ground operations inside Gaza to wipe out the ruling Islamist Hamas movement following its surprise attack three weeks ago that Israeli authorities say killed more than 1400 people.
"Over the last day, combined IDF combat 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 organisation," the Israel Defence Forces (IDF) said in a statement.
Militants responded with anti-tank missiles and machine gun fire, it added.
Israeli armed forces also bombed Gaza overnight in air, sea and ground attacks, targeting northwestern areas of the Palestinian enclave where Israeli troops were operating on the ground, witnesses said.
The United States and Arab countries have urged Israel to delay any ground operation that would multiply the number of civilian casualties and might ignite a wider conflict.
Air raid sirens went off in the area of the Israeli Red Sea city of Eilat on Tuesday and Israel's military said it downed an approaching "aerial target".
"There was no threat or risk to civilians," it added.
Witnesses said Israeli forces targeted Gaza's main north-south road on Monday and attacked Gaza City from two directions. Israel said its troops freed a soldier from Hamas captivity.
Hamas has so far released four civilians from the 240 hostages Israel says were captured in the October 7 attacks. Many of the hostages are believed to held in the tunnels.
The al-Qassam Brigades, Hamas's armed wing, said militants clashed early on Tuesday with Israeli forces "invading the southern Gaza axis," adding that four vehicles were targeted with al-Yassin 105 missiles, referring to locally produced anti-tank missiles.
Reuters was unable to confirm the reports of fighting. Israel's military had no immediate comment.
Gaza health authorities say 8306 people, including 3457 minors, have been killed in Israeli attacks since October 7. UN officials say more than 1.4 million of Gaza's civilian population of about 2.3 million have been made homeless.
The mounting death toll has drawn calls from the US, Israel's top ally, other countries and the UN for a pause in fighting to allow more humanitarian aid to reach the enclave.
Netanyahu said 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.
Israel's military said it struck more than 600 militant targets in recent days in Gaza, where civilians are in dire need of fuel, food and clean water.
Israeli air strikes on Monday night outside the Indonesian Hospital in the northern Gaza Strip caused a power cut and doctors said they feared for the lives of 250 injured Palestinians being treated there as fuel runs low.
"Running out of fuel would mean no power and no power would mean the inevitable death of many patients at intensive care unit and wounded in surgery departments," Dr. Moaeen Al-Masri said.
The UN humanitarian office (OCHA) said water supply through a pipeline from Israel to southern Gaza was cut off on Monday "for unknown reasons", and that an announced repair of another pipeline to central Gaza did not take place.
Significantly fewer humanitarian aid trucks than needed have reached the besieged enclave, UN officials said, and civil order has broken down with people storming UN warehouses in search of food.
That has put four UN aid distribution centres and a storage facility out of action, the United Nations agency for Palestinian refugees (UNRWA) said on Monday.
"It's a disaster on top of a disaster. Health needs are soaring and our ability to meet those needs is rapidly declining," World Health Organisation regional emergencies chief Rick Brennan said, reiterating international calls for a ceasefire to enable a larger humanitarian operation.
Aid trucks have been trickling into Gaza from Egypt over the past week via Rafah, the main crossing that does not border Israel. It has become the main point of aid delivery since Israel imposed a "total siege" of Gaza after October 7.
Australian Associated Press