Israeli air strikes and ground operations were focused Thursday on the Gazan city of Khan Yunis, where the UN said nine people were killed by tank shelling at one of its shelters the day before.
The deadly incident came after the Israeli army said it had encircled the city, where footage released by the military showed soldiers engaged in urban combat amid ruined buildings.
Hamas's press office also reported fierce clashes in the center and west of Khan Yunis, while its health ministry counted multiple deaths overnight from strikes in the city and elsewhere in the territory.
It said four children were killed in the Nuseirat camp in an early morning bombardment on Thursday.
Wednesday's attack on the UN shelter for displaced people saw the site hit by two tank rounds, killing nine and injuring 75, said Thomas White, the Gaza head of the UN agency for Palestinian refugees, UNRWA.
UNRWA chief Philippe Lazzarini said the number of dead was likely to rise.
"Once again a blatant disregard of basic rules of war," Lazzarini said on the social media platform X, adding that the compound had been clearly marked as a UN facility and its coordinates had been shared with Israeli authorities.
James McGoldrick, interim UN humanitarian coordinator for the Palestinian territories, told reporters that "buildings were ablaze" at the shelter in the aftermath of the strike, AFP reported.
"Many people are trying to flee the scene but unable to do so," he said.
The United States condemned the attack, with State Department spokesman Vedant Patel saying "civilians must be protected and the protected nature of UN facilities must be respected".
The Gaza war began with Hamas's unprecedented October 7 attack. In response, Israel has carried out a relentless military offensive that has killed at least 25,700 people in Gaza, about 70 percent of them women and children, according to the health ministry in the Hamas-run territory.
In the southern border town of Rafah on Wednesday, Palestinians inspected the damage after a strike on a mosque, which had been reduced to rubble.
"We headed to Rafah based on (Israeli) instructions that it is a safe zone, only to discover that it is just like other areas," Mohammed Barbakh, who had been displaced from Khan Yunis, told AFP.
The government of Prime Minister Benjamin Netanyahu has faced mounting calls for a ceasefire, with domestic pressure intensifying after 24 soldiers were killed Monday in the army's deadliest single day since it launched ground operations in Gaza.
Citing Israeli officials, the New York Times said 21 of those soldiers were killed in an operation to demolish part of a Palestinian neighbourhood in order to create a "buffer zone" inside Gaza along the Israeli border.
In Tel Aviv, Israeli protesters carried a banner saying "Stop the bloodshed" and blocked a road during a demonstration to demand a deal for the release of the hostages held by Hamas.
"We came to say to the government, 'It's enough.' We want all the hostages back home, we want a ceasefire now," said protester Sapir Sluzker Amran.
"There is no military solution, only a diplomatic solution -- only agreements will bring the hostages back."
Netanyahu, however, has been adamant the war will continue, telling parliament on Wednesday that the fighting would persist until the "aggression and evil" of Hamas were destroyed.
"This is a war for our home," he said.
