Israel levelled a northern Gaza district on Friday after giving families a half-hour warning to escape, and hit an Orthodox Christian church where others had been sheltering, as it made clear that a command to invade Gaza was expected soon.

In Washington, U.S. President Joe Biden, back from a trip to Israel to demonstrate support, asked Americans in a televised speech to spend billions more dollars to help Israel fight Hamas, which he said sought to "annihilate" Israel's democracy.

Israel has vowed to wipe out the Hamas Islamist group that rules Gaza, after its gunmen burst through the barrier fence surrounding the enclave on Oct. 7 and rampaged through Israeli towns and kibbutzes, killing 1,400 people, mainly civilians.

"You see Gaza now from a distance, you will soon see it from inside. The command will come," Defense Minister Yoav Gallant told troops gathered at the Gaza border on Thursday.

Israel has pounded Gaza with air strikes and put the enclave's 2.3 million people under a total siege, banning shipments even of food, fuel and medical supplies. Since Oct. 7, 3,785 Palestinians have been killed including more than 1,500 children, Palestinian officials say. The U.N. says more than a million have been made homeless.

Israel has already told all civilians to evacuate the northern half of the Gaza Strip, which includes Gaza City. Many people have yet to leave saying they fear losing everything and have nowhere safe to go with southern areas also under attack.

The Orthodox Patriarchate of Jerusalem, the main Palestinian Christian denomination, said Israeli forces had struck the Church of Saint Porphyrius in Gaza City, where hundreds of Christians and Muslims had sought sanctuary.

Video from the scene showed a wounded boy being carried from rubble at night. A civil defense worker said two people on upper floors had survived; those on lower floors had been killed and their bodies were still in the rubble.

"They felt they would be safe here. They came from under the bombardment and the destruction, and they said they would be safe here but destruction chased them," a man cried out.

Gaza's Hamas-run government media office said 18 Christian Palestinians had been killed. There was no immediate word from the church on the final death toll. It said targeting churches that were used as shelters for people fleeing bombing was "a war crime that cannot be ignored."

The Israeli military said part of the church was damaged in a strike on a militant command center and it was reviewing the incident.

In Zahra, a northern Gaza town, residents said their entire district of some 25 multi-storey apartment buildings was razed to the ground.

They received Israeli warning messages on their mobile phones at breakfast time, followed ten minutes later by a small drone strike that hammered the message home. Half an hour after the initial warning, F-16 warplanes brought the buildings down in huge explosions and clouds of dust.

"Everything I ever dreamt of and thought that I have achieved was gone. In that apartment was my dream, my memories with my children, and my wife, was the smell of safety and love," Ali, a resident of the district, told Reuters by phone, declining to give his full name for fear of reprisals.

The United Nations humanitarian affairs office said more than 140,000 homes - nearly a third of all homes in Gaza - have been damaged, with nearly 13,000 completely destroyed.

The south of the enclave has also been regularly hit. Gaza authorities said there were several dead and wounded in fresh strikes on Khan Younis, the enclave's main southern city.

OTHER FRONTS IN LEBANON, WEST BANK

While Israeli troops are massing around Gaza in anticipation of an order to invade, conflict is also spreading to two other fronts - the West Bank and the northern border with Lebanon.

The defense ministry ordered residents of the largest Israeli town near the Lebanese border, Kiryat Shmona, to evacuate to guest houses. Clashes at the border between Israel and Lebanon's Hezbollah movement have been the deadliest since a full-blown war in 2006.

In the West Bank, the Palestinian health ministry said 13 people were killed including five children after Israeli troops raided and called in air strikes on the Nur Shams refugee camp near Tulkarm.

The territory, where Palestinians have limited self rule under Israeli military occupation, has seen the deadliest clashes since the second intifada uprising ended in 2005.

Diplomats fear the conflict could spread even further. The Pentagon on Thursday said a U.S. Navy warship operating in the northern Red Sea intercepted three cruise missiles and several drones launched by the Houthi movement in Yemen, potentially toward Israel.

The Houthi, like Hamas in Gaza and Lebanon's Hezbollah, are backed by Iran, which has lauded the Hamas attacks on Israel though it denies being behind them.

AID TO GAZA STILL HELD UP

Western leaders have so far mostly offered support to Israel's campaign against Hamas, although there is mounting unease about the plight of civilians in Gaza, which has yet to receive long promised aid.

"We can't ignore the humanity of innocent Palestinians who only want to live in peace and have opportunity," Biden said in his speech.

Israel has said it will allow no aid from its own territory to reach Gaza until more than 200 hostages captured by the gunmen are set free, a position Palestinians say amounts to unlawful collective punishment of the civilian population.

Biden secured a promise from Israel to allow some aid to enter Gaza from Egypt, provided it is monitored to ensure none reaches Hamas. So far, the trucks remain backed up on the Egyptian side of the crossing.