At least 42 were killed in Israeli attacks on Gaza's Al-Tuffah and Al-Shati districts, Ismail Al-Thawabta, the director of the Hamas-run government media office told Reuters.
The Israeli military released a brief statement saying: "A short while ago, IDF fighter jets struck two Hamas military infrastructure sites in the area of Gaza City."
It said more details would be released soon.
It comes after the International Committee of the Red Cross said 22 people were killed in shelling that damaged its Gaza office today, as the Israeli army intensified strikes in the besieged Palestinian territory.
Exchanges of fire across the Lebanese border between Israel and the powerful Iran-backed militant group Hezbollah have also escalated in recent weeks, raising fears of an even wider war.
UN Secretary-General Antonio Guterres said yesterday that the cross-border hostilities must not turn Lebanon into "another Gaza", warning of the risk of triggering a catastrophe "beyond imagination".
His warning came as Israel stepped up its strikes in Gaza, where one hospital in Gaza City reported at least 30 dead.
Further south, the ICRC said 22 bodies and 45 wounded people were taken to a Red Cross field hospital after shelling with "heavy calibre projectiles" near its Gaza office, which was surrounded by displaced people living in tents.
"Firing so dangerously close to humanitarian structures puts the lives of civilians and humanitarians at risk," the ICRC said on social media platform X.
The health ministry in the Hamas-run territory blamed the shelling on Israel, saying there were 25 killed and 50 wounded in the Al-Mawasi area near the ICRC office, not far from Rafah.
An Israeli Defense Force spokesman did not acknowledge any role in the incident but said it was "under review".
'A difficult and brutal day'
In the north of Gaza, the director of Gaza City's Al-Ahli hospital was quoted by the territory's health ministry as reporting 30 dead in strikes.
"It has been a difficult and brutal day in Gaza City. So far, around 30 martyrs have arrived at the Al-Ahli Arab Hospital," doctor Fadel Naeem was quoted as saying.
Civil defence agency spokesman Mahmud Basal said five municipal workers died when a garage in the city was bombed.
Israel's military reported operations yesterday "north and south of the Central Gaza Strip Corridor".
The operations around Gaza coincided with flaring hostilities along the Lebanese border.
Lebanon-based Hamas ally Hezbollah said it had fired dozens of rockets at a barracks in northern Israel on Thursday in retaliation for a deadly air strike in south Lebanon.
Israel said a Hezbollah operative was killed in that strike.
Hezbollah also claimed a number of attacks on Israeli troops and positions near the border on Friday, including two using drones.
The Israeli army said it had carried out multiple retaliatory strikes on both days.
Israeli jets yesterday struck a "Hezbollah military structure in the area of Khiam, a Hezbollah military post in the area of Meiss El Jabal, and Hezbollah terrorist infrastructure in the areas of Taybeh and Tallouseh in southern Lebanon", the army said in a statement.
Experts are divided on the prospect of a wider war, almost nine months into Israel's campaign to eradicate Hamas in Gaza.
Amid the escalating exchanges between Israel and Hezbollah, Israel's military said Tuesday that plans for an offensive in Lebanon had been "approved and validated".
Hezbollah chief Hassan Nasrallah said "no place" in Israel would "be spared our rockets" in a wider war, and also threatened nearby European Union member Cyprus.
Citing the "bellicose rhetoric" on both sides, UN chief Guterres said that the risk of all-out war was real.
"One rash move - one miscalculation - could trigger a catastrophe that goes far beyond the border, and frankly, beyond imagination," he said.
Israel's ally the United States has appealed for de-escalation.
