Dozens of Palestinians were killed in Gaza on Saturday in air strikes by Israel, Palestinian media said, after the U.S. urged Israel to scale down its military campaign and narrowly target Hamas leaders.

At least 14 people died from strikes that hit two houses on Old Gaza Street in Jabalia, and dozens were killed in a strike that hit another home in Jabalia, the official WAFA news agency said.

The Palestinian agency reported a large number of civilians were trapped under rubble.

Israeli military said its aircraft targeted a building in Jabalia after its forces come under fire and a number of Hamas militants were identified on the roof. It was unclear if the building was one of those that WAFA reported hit.

The military said its forces killed militants holed up in two schools in Gaza City and raided apartments in Khan Younis stocked with weapons, and uncovered what it described as undergound infrastructure used by Hamas.

Reuters could not independently verify the reports.

With intense ground fighting across the narrow Gaza Strip and aid organisations warning of a humanitarian catastrophe, the United States has warned that Israel risks losing international support because of "indiscriminate" air strikes killing Palestinian civilians.

President Joe Biden's national security adviser, Jake Sullivan, visiting Israel on Thursday and Friday, carried a message to Israel to scale down the broad military campaign and transition to more narrowly targeted operations against Hamas leaders, U.S. officials said.

During Sullivan's visit, Israeli officials publicly emphasised that they would continue the war until they achieve their aim of eradicating Hamas, which may take months.

Washington hinted on Friday at disagreement with Israel over how quickly to scale down the war, with Sullivan saying the timing was the subject of "intensive discussion" between the allies.

In a surprise cross-border attack on Israel on Oct. 7, Hamas militants rampaged through Israeli towns killing 1,200 people and capturing 240 hostages. Israel's counterattack has killed close to 19,000 people, according to Gaza health authorities, with thousands more feared buried under rubble.

Israel's military said on Friday it killed three hostages held by Hamas in Gaza after wrongly identifying them as a threat. The military expressed condolences to the families of the hostages killed during combat, saying there would be "full transparency" in an investigation into the incident.

The military said it had recovered the bodies of three other hostages killed by Hamas. Israel says it believes around 20 of more than 130 hostages still held in densely populated coastal strip are dead.

Combat has intensified in the past two weeks since a week-long truce collapsed.

Israeli government spokesperson Eylon Levy said Israel was winning the war and degrading Hamas, citing a reduction in the number of rockets fired into Israel.

But hours later and for the first time in weeks, there were sirens in Jerusalem and explosions overhead from at least three interceptions by Israel's Iron Dome air defences. The armed wing of Hamas claimed responsibility for the rocket attack it called a response to "Zionist massacres against civilians".

The vast majority of Gaza's 2.3 million people have been driven from their homes over the past two months, many several times.

After Sullivan left, Israel said it would open the Kerem Shalom crossing, the main road link into Gaza, for aid shipments for the first time in the war, allowing 200 trucks in per day, double the capacity at Rafah.

Aid agencies, warning of mass starvation and disease, had long pleaded for Israel to speed up deliveries by letting aid enter directly at Kerem Shalom on the border of Egypt, Israel and Gaza.

Gaza residents reported another night of intense fighting and bombardment the length of the enclave on Friday, including in Sheijaia, Sheikh Radwan, Zeitoun, Tuffah and Beit Hanoun in the north, and in the centre and northern fringes of the main southern city Khan Younis.

"The Gaza Strip turned into a ball of fire overnight, we could hear explosions and gunshots echoing from all directions," Ahmed, 45, an electrician and father of six, told Reuters from a shelter in central Gaza.

"They can destroy homes and roads and kill civilians from the air or through blind tank shelling, but when they come face to face with the resistance, they lose."