The Israeli army said Monday that its forces killed dozens of militants in clashes through the night in Gaza as it presses on with its military response to the 7 October Hamas attacks.

The army said "troops killed dozens of terrorists who barricaded themselves in buildings and tunnels and attempted to attack the troops", and that a fighter jet had targeted a building "with over 20 Hamas terrorist operatives inside".

Hamas earlier said it was engaged in "heavy fighting" with Israeli troops inside northern Gaza, where besieged residents were again told to flee.

After weeks of ferocious air strikes, Israeli Prime Minister Benjamin Netanyahu has declared a new "stage" in what he warned will be a "long and difficult" war.

Israel's military released a series of images late Sunday purporting to show tanks, armoured personnel carriers, artillery and equipment-laden infantrymen operating inside Palestinian territory.

Hamas said its Ezzedine al-Qassam Brigades were already "engaged in heavy fighting... with the invading occupation forces".

The Israel Defence Forces claimed to have struck more than "450 terror targets, including operational command centres, observation posts, and anti-tank missile launch posts".

The military also said 31-year-old sergeant Yinon Fleishman, a reservist, was killed in northern Israel when his tank overturned.

With a fierce urban war now feared in Gaza, Israeli army spokesman Daniel Hagari told Palestinian civilians to go south "to a safer area".

"We are gradually expanding the ground activity and the scope of our forces in the Gaza Strip," he said.

It is now more than three weeks since Hamas gunmen launched a wave of bloody cross-border raids against homes, communities, farms and security posts inside Israel.

An estimated 1,400 people, mostly civilians, were killed and 239 people were taken hostage, according to the latest Israeli tallies.

Grieving and enraged, Israel has vowed to free the hostages, track down those responsible and "eradicate" Hamas, a Palestinian Islamist movement that has governed Gaza since 2007.

But there is growing international concern about the toll of Israel's campaign on Gaza's 2.4 million residents.

The territory is under siege, with people unable to leave and only a trickle of humanitarian aid allowed in.

Meanwhile, Israel has carried out one of the most intense bombing campaigns in recent memory.

Gaza's Hamas-run health ministry says more than 8,000 people, mainly civilians, have been killed, many of them children.

- Food, water, medicine -

Inside Gaza's maze of streets, rubble and hulled-out buildings, there is a growing sense of panic, fear and desperation.

Ibrahim Shandoughli, a 53-year-old from Jabaliya in northern Gaza, asked why he would head south when that area is also being bombed.

"Where do you want us to evacuate to? All the areas are dangerous," he said.

Etidal al-Masri was among those who did move south.

But even in the border town of Rafah, she still struggles to find even the basics amid shortages of food, water and medicine.

Gazans "must now queue for bread, toilets and even for sleep", she said.

On Sunday, the desperation appeared to boil over.

The United Nations reported that "thousands of people" had ransacked its warehouses looking for tinned food, flour, oil and hygiene supplies.

The UN also reported that 33 trucks carrying water, food and medical supplies had entered Gaza from Egypt on 29 October.

It is one of the largest deliveries to date, but still far short of the 100 trucks a day that aid groups say is needed.

International Criminal Court lead prosecutor Karim Khan warned Israel on Sunday that preventing access to humanitarian aid could be a "crime".

- 'Axis of resistance' -

In a phone call with Netanyahu on Sunday, US President Joe Biden also underscored the need to "immediately and significantly" increase the flow of aid.

And while the White House has welcomed the gradual return of cell phone and internet services that had been cut for days, it had a sharp warning for Israel's leaders.

The "burden" lies with Israel to distinguish between militants and innocent civilians in Gaza, US National Security Advisor Jake Sullivan told CNN.

According to the UN, all 10 hospitals in northern Gaza have received evacuation orders -- despite sheltering thousands of patients and about 117,000 of the displaced.

The Palestinian Red Crescent Society has said evacuation is impossible and reported repeated strikes around Al-Quds hospital in central Gaza.

The head of the World Health Organization said calls to evacuate Al-Quds hospital were "deeply concerning".

"We reiterate -- it's impossible to evacuate hospitals full of patients without endangering their lives," Tedros Adhanom Ghebreyesus wrote on X.

Mohamed al-Talmas, who has taken shelter in Gaza's biggest hospital Al-Shifa, said "the ground shook" there with intense Israeli raids.

Israel describes Al-Shifa hospital as a de facto Hamas "command centre" and headquarters.

Washington has also expressed deep concern about the war spilling over, as Israel's enemies -- and in particular an Iran-allied "axis of resistance" -- step up actions across the Middle East.

Iran's President Ebrahim Raisi has warned Israel's "crimes have crossed the red lines, which may force everyone to take action".

Since Hamas's attack on 7 October, Iran-backed groups have launched attacks from Lebanon, Yemen, Iraq and Syria.

Skirmishes have intensified on the Israeli-Lebanese border with Iran-backed Hamas ally Hezbollah.

On Sunday militants in south Lebanon fired rockets towards Israel, which has responded with strikes.

The Israel Defense Forces also said they had "struck military infrastructure in Syrian territory" in response to launches "toward Israeli territory."

- 'Psychological games' -

Inside Israel, where shocked residents still face daily rocket attacks, much of the focus is on the hostages abducted by Hamas.

Hamas has released four prisoners and offered to release more as part of a swap for Palestinians detained in Israel.

It has also claimed "almost 50" hostages were killed by Israeli strikes -- a claim that was impossible to verify but has caused anguish to those praying for their loved ones to return.

"We demanded that no action be taken that endangers the fate of our family members," said Meirav Leshem Gonen, the mother of hostage Romi Gonen.

Israel's Defence Minister Yoav Gallant accused Hamas of playing "psychological games".

"Hamas is cynically using those who are dear to us -- they understand the pain and the pressure," he said.

AFP