Several explosions and gunfire have been reported in northern Gaza as Israel said it has resumed its attacks on the besieged strip after a temporary ceasefire expired.
Palestinian media outlets also reported fierce clashes between Israeli forces and Palestinian resistance fighters on Friday.
The Gaza-based interior ministry said Israel launched artillery strikes on the northwestern part of the Gaza Strip. A series of airstrikes also hit the besieged strip.
Marwan al-Hams, the director of al-Najar hospital in Rafah in southern Gaza, where many Palestinians fled after being told by Israel to leave the north of the territory, said strikes killed at least nine people in the city, including four children.
Residents said the Israeli military had distributed leaflets over the city of Khan Younis and its surrounding areas in the south, declaring them a war zone and telling residents to move to Rafah.
Heath ministry spokesperson in Gaza Ashraf al-Qudra confirmed that the death toll had risen to 32 Palestinians.
Qudra said the dead included ten people killed in al-Maghazi in central Gaza, nine in Rafah in the South, and five in Gaza City in the north - hours after the truce ended at 7 a.m. local time (0500 GMT) .
UNICEF spokesperson James Elder described the scenes at a hospital in Gaza, saying "this is a war on children".
"Inaction by those with influence is allowing the killing of children," he told reporters in Geneva via video-link from Gaza. "It is reckless to think more attacks on the people of Gaza will lead to anything other than carnage."
Sirens were sounded in several Israeli settlements near Gaza as the Israeli regime claimed it had intercepted a rocket fired from Gaza. Israeli authorities said they were restarting emergency measures in the area including closing schools.
In the north of the Gaza Strip, the fireball from a large explosion could be seen from across the border in the Israeli city of Sderot, AFP reported. Local authorities said a rocket launched from the Gaza Strip caused damage to property in Kibbutz Mefalsim.
The al-Quds Brigades, the armed wing of the Palestinian Islamic Jihad movement (PIJ), said it attacked Israeli cities and towns on Friday morning in response to "crimes against our people".
The truce, which was extended twice, began on November 24. It had paused brutal Israeli strikes on Gaza that began in early October.
International bodies have called for more time to get medical supplies, food and fuel into Gaza, where an estimated 1.7 million people have been forced from their homes.
The fighting resumed after US top diplomat Antony Blinken visited the region and held talks with Israeli leaders. Other world leaders, and aid groups, had sought an extended pause.
Hamas top official Osama Hamdan said the "responsibility for not extending the ceasefire lies with the Zionist regime and the United States".
He said the Palestinian resistance was seriously looking for a ceasefire and is still pursuing it.
Ezzat al-Rashq, a member of the Hamas political bureau, said: "What Israel did not achieve in the 50 days before the ceasefire, it will not achieve with the continuation of its aggression."
Israel launched the war on Gaza on October 7 after the Palestinian resistance movement Hamas waged the surprise Operation Al-Aqsa Storm against the occupying entity in response to the Israeli regime's decades-long campaign of bloodletting and devastation against Palestinians.
Tel Aviv also blocked water, food, and electricity to Gaza, plunging the coastal strip into a humanitarian crisis.
More than 15,000 Palestinians, most of them women and children, have been killed in the Israeli strikes.
The Israeli violence in Gaza has also raised tensions in the West Bank, where nearly 240 Palestinians have been killed by soldiers or settlers since October 7, according to the Ramallah-based Palestinian health ministry.
The truce saw the release of 105 Israeli captives held in Gaza and 240 Palestinian prisoners.
The ceasefire had allowed some humanitarian aid into Gaza but the aid supplies were far below what is needed, according to aid workers.