Hamas has handed over more bodies of dead hostages to Israel, and US President Donald Trump has warned the militant group must now disarm or be forced to "quickly and perhaps violently".
The bodies were returned after Israel earlier accused Hamas of violating the ceasefire agreement by not returning all of the dead hostages' remains.
It announced it would halve the number of humanitarian aid trucks allowed into Gaza as punishment.
Meanwhile, re-emergent Hamas fighters demonstrated they were reasserting control in Gaza by deploying hundreds of security forces in the streets and executing several people they accused of collaborating with Israel.
Earlier in the day, the prospects for Mr Trump's peace plan appeared to darken when the president warned Hamas it must disarm or be forced to.
"If they don't disarm, we will disarm them. And it will happen quickly and perhaps violently," Mr Trump said at the White House, one day after he spoke before the Knesset in Jerusalem.
"I spoke to Hamas, and I said, 'You're going to disarm, right?'
"'Yes, sir, we're going to disarm.' That's what they told me," Mr Trump said, later clarifying that he had passed the message through intermediaries.
Israeli Prime Minister Benjamin Netanyahu has maintained the war cannot end until Hamas surrenders its weapons and cedes control of Gaza, a demand the militant group has rejected.
Hamas has not publicly committed to laying down its weapons.
More bodies of hostages returned
Mr Trump proclaimed the "historic dawn of a new Middle East" while speaking to Israel's parliament on Monday as Israel and Hamas were exchanging the last 20 living Israeli hostages in Gaza for nearly 2,000 Palestinian detainees and prisoners.
The prisoner and hostage exchange was "phase one" of a US-led peace plan between Israel and Hamas.
Overnight the US president declared that "phase two" of the Gaza ceasefire had begun, and called out Hamas for not returning all of the dead hostages.
"A big burden has been lifted, but the job is not done. The dead have not been returned, as promised!" he said in a social media post.
"Phase two begins right now!"
The return of 28 dead hostages has remained one of the final details to be worked out in the deal to end more than two years of conflict that began with Hamas's attacks on Israel on October 7, 2023.
Hamas has now handed over eight coffins carrying dead hostages, leaving at least 19 hostages presumed dead and one unaccounted-for in the Gaza Strip.
Earlier, the families of hostages accused Hamas of reneging on the deal, which stipulated the group must hand over all remaining hostages, dead or alive, within 72 hours of the ceasefire starting at midday on Monday.
The militant group said locating the bodies would be difficult due to the rubble, a caveat already acknowledged by Mr Trump, who steered the ceasefire deal.
Some reports also suggest Israel informed hostage families months ago that it could be difficult to recover the bodies.
On Tuesday, local time, the Israeli military said it received four coffins from the Red Cross at a meeting point in the northern part of the Gaza Strip. Those coffins, escorted by Israeli forces, crossed the border into Israel shortly before midnight and were being taken for forensic identification, the Israeli military said.
Hamas also confirmed the transfer was underway.
Like the hostages' families, Israeli officials had also earlier said that Hamas had violated the ceasefire deal by failing to turn over the bodies of all the hostages.
In response, the Israeli officials said, they had decided to restrict aid, allowing only half the agreed number of aid trucks into Gaza starting Wednesday, and to delay plans to open the southern border crossing to Egypt.
It was unclear whether the release of four more bodies changed those plans.
The ceasefire has largely held since the hostage and prisoner exchange on Monday, but the Israeli military has killed six Palestinians since then.
Drone fire killed five people as they went to check on houses in a suburb east of Gaza City, and an air strike killed one person and injured another near Khan Younis, the Gaza Health Ministry said.
The IDF said it opened fire on Tuesday to remove a "threat" posed by "suspects" who approached its forces in the northern Gaza Strip.
It said they had crossed truce lines and approached its forces after ignoring calls to turn back, in a violation of the deal.
Hamas accused Israel of violating the ceasefire.
Video emerges of Hamas shooting 'collaborators'
Meanwhile, Hamas has swiftly reclaimed Gaza's urban areas following the partial withdrawal of Israeli troops last week.
The militant group has sent its men back into the streets of Gaza since the ceasefire began on Friday, moving cautiously in case it suddenly collapsed, two security sources in the territory told Reuters.
In a video circulated late on Monday, Hamas fighters dragged seven men whose hands were tied behind their backs into a Gaza City square, forced them to their knees and shot them from behind as dozens of onlookers watched from nearby storefronts.
The video was verified by media outlets including Reuters and the BBC. In the footage, the executed men are referred to as "collaborators".
Mr Trump has previously given his blessing to Hamas to reassert some control of Gaza, at least temporarily.
The video of the executions was widely shared on social media, including by Israel's Foreign Ministry, which said it demonstrated why "Hamas must go".
Palestinian security officials said dozens of people had been killed in clashes between Hamas fighters and rivals in recent days.
Hamas sources told Reuters on Tuesday the group would not tolerate more violations of order in Gaza and it would target collaborators, armed looters and drug dealers.
The ceasefire has, for now, stopped two years of devastating warfare in Gaza triggered by the October 7, 2023, attack in which Hamas-led gunmen killed about 1,200 people and took 251 hostages back to Gaza, according to Israeli tallies.
Israel's military has killed at least 67,000 people in Gaza, according to local health authorities, with thousands more feared dead under the rubble.
Gaza's Civil Defence Service said 250 bodies had been recovered since the truce began.
ABC/Reuters
