Prime Minister Benjamin Netanyahu said on Saturday that Israeli forces had unleashed the second phase of the Gaza war as they pressed ground operations against Hamas militants, vowing to "destroy the enemy above ground and below ground."

Gaza's besieged people had barely any communications with the outside world as Israeli jets dropped more bombs on the Hamas-ruled Palestinian enclave and military chiefs said a long-threatened ground offensive was gearing up.

Speaking at a press conference in Tel Aviv, Netanyahu warned Israelis to expect a "long and hard" military campaign but stopped short of calling the current Israeli ground incursions a full-scale invasion.

He reiterated Israel's appeal to Palestinian civilians to evacuate the northern Gaza Strip where Israel was focusing its attack, and vowed that every effort would be made to rescue the more than 200 hostages held by Hamas.

"This is the second stage of the war whose goals are clear - to destroy Hamas' governing and military capabilities and to bring the hostages home," Netanyahu told reporters.

"We are only at the start," he said. "We will destroy the enemy above ground and below ground."

Israel has blockaded and bombarded Gaza for three weeks after the Islamist group Hamas' Oct. 7 assault killed 1,400 Israelis in the deadliest day of the nation's 75-year history.

Western countries have generally backed what they say is Israel's right to self defence but there has been mounting international concern over the toll from the bombing and growing calls for a pause to allow aid to reach Gaza civilians.

Health authorities in the Gaza Strip of 2.3 million people say 7,650 Palestinians have been killed in Israel's campaign to obliterate the militants.

Palestinian President Mahmoud Abbas, whose Palestinian Authority governs parts of the occupied West Bank while Hamas rules Gaza, said, “Our people in the Gaza Strip are facing a war of genocide and massacres committed by the Israeli occupation forces in full view of the entire world.”

With many buildings reduced to rubble and shelter hard to find, Gazans are short of food, water, fuel and medicines. Their plight got worse from Friday night when phone and internet services were cut - followed by heavy bombing through the night.

"God help anyone under the rubble," said one Gaza journalist, who spent a terrifying night in a building stairway watching "belts of fire" as bombs fell and Israeli forces appeared to exchange fire with Palestinian fighters.

Without mobile phones, no one could call ambulances and emergency services anyway were short of fuel, he said.

Israel's chief military spokesperson declined to say whether Israel was behind the telecommunications blackout in Gaza but said it would do what it needed to protect its forces.

ISRAELI TROOPS TARGET TUNNELS

Though there was no indication of an invasion en masse, Israel said troops and armour sent into Gaza on Friday night were still in the field, focusing on infrastructure including the extensive tunnel network built by Hamas.

In calling on Gazans to move south, Israel said Hamas was hiding under civilian buildings, especially in the north. Palestinians say nowhere is safe, with bombs also smashing homes in the south of the densely populated territory.

"A humanitarian catastrophe is unfolding in front of our eyes," U.N. Secretary-General Antonio Guterres said.

Various global aid agencies said they could not contact their staff in Gaza. But a representative from the International Committees of the Red Cross and Red Crescent in Gaza, William Schomburg, got an audio message out.

Schomburg said medics were working around the clock while also facing personal tragedies. "I spoke to one doctor who had lost his brother and cousin the night before," he told the BBC broadcaster in a clip the ICRC posted on X.

Billionaire entrepreneur Elon Musk offered his Starlink satellite network to support communications in Gaza for internationally recognised aid organisations.

Video from the Israeli side of the heavily fortified fence showed explosions in Gaza sending up clouds of smoke among a line of ruined buildings.

Hamas said on Saturday that it had been about to reach an agreement with Israel over the more than 200 hostages it has in Gaza, but Israel "stalled" on that.

Israel's military spokesman dismissed the reports, saying Hamas was "cynically" attempting to sway public opinion.

Netanyahu, who met with hostages' families earlier on Saturday, said contacts to secure their release would continue even during a ground offensive and that military pressure on Hamas could help bring them home. He did not elaborate.

Qatar-mediated negotiations between Israel and Hamas aimed at de-escalating the fighting continued on Saturday but at a much slower pace, a source briefed on the talks said.

Jets killed the head of Hamas' aerial wing, Asem Abu Rakaba, a key figure in the Oct. 7 attack, Israel's military said.

REGIONAL 'TIME BOMB'

Warplanes struck 150 underground targets in north Gaza, including Hamas tunnels, underground combat spaces and other underground infrastructure, killing others from the group, the Israeli military said.

The armed wing of Hamas, the al-Qassam brigades, said its fighters were battling Israeli troops in Gaza's northeastern town of Beit Hanoun and in the central area of Al-Bureij.

"Al-Qassam Brigades and all Palestinian resistance forces are fully prepared to confront the aggression with full force and thwart the incursions," it said.

The United States and other Western countries had urged Israel to hold off on a ground offensive for fear of high Palestinian casualties and a widening conflict.

Hamas is backed by Iran, which also supports militias in Lebanon, Syria, Iraq and Yemen. U.S. troops have come under fire from Iran-backed groups in Iraq and Syria. Washington has been moving more military assets to the region.

Israeli Defence Minister Yoav Gallant told reporters Israel had no interest in expanding the war beyond Gaza but is prepared on all fronts.

The Israeli military reported a new exchange of fire on the border with Lebanon on Saturday, the latest in what have been the most serious clashes on the border since 2006.

The crisis brought hundreds of thousands of pro-Palestinian demonstrators out in cities around Europe, the Middle East and Asia on Saturday.

"This is not about Hamas. This is about protecting Palestinian lives," said marcher Camille Revuelta in London.