Israeli aircraft struck Gaza while Palestinians fired rockets at Israel on Saturday after an Israeli operation against the Islamic Jihad militant group in the Gaza Strip ended more than a year of calm along the border.
The Israeli strikes have killed 24 people - including six children - and left more than 200 injured, authorities in Gaza say.
On Saturday, Israel said it struck Islamic Jihad militants preparing to launch rockets. Additional bombings aimed at three houses, witnesses said, flattening at least one as the sounds of more explosions rocked Gaza City.
Palestinian news agency Wafa said air strikes destroyed two buildings on Saturday — one in Gaza City and another to the west — leaving more than 100 people homeless. Warnings were given to the residents shortly before both attacks, it said.
Targets in Khan Yunis in the southern Gaza Strip were also hit, Wafa said.
But Israel said it has "irrefutable" evidence that stray rocket from Islamic Jihad militants was responsible for the death of multiple children in Jabalia, northern Gaza, on Saturday.
The Israeli army said it was prepared for a “week of fighting” against Islamic Jihad in the Gaza Strip.
The military said it apprehended 19 Islamic Jihad militants in overnight raids in the occupied West Bank and it was aiming at the group's rocket manufacturing sites and launchers in Gaza.
Defence Minister Benny Gantz said the military was conducting operations to remove Islamic Jihad's threat and "restore peace and stability in Israel's south".
Palestinian militants fired at least 160 rockets across the Gaza border on Saturday, setting off air raid sirens and sending people running to bomb shelters as far away as the central Israeli city of Modiin, between Tel Aviv and Jerusalem.
Islamic Jihad said it had aimed at Israel's main international gateway, Ben Gurion Airport, but the rocket fell short near Modiin, about 20 kilometres away. Israel's Civil Aviation Authority said the airport was operating as usual with flight routes adjusted.
Air raid sirens also sounded in the southern city of Sderot and several other towns near the border with the Gaza Strip, Israeli media reported.
Most of the missiles were intercepted and there were no reports of serious casualties, according to the Israeli ambulance service.
The UN humanitarian chief for the occupied Palestinian territories, Lynn Hastings, urged the warring sides to allow "fuel, food, and medical supplies" to be delivered to Gaza amid the worsening crisis.
Egypt's Foreign Ministry said Cairo was "conducting contacts" with the aim of containing the situation in Gaza, bringing calm and protecting lives and property.
UN Middle East peace envoy Tor Wennesland said he was "deeply concerned" and gave a warning that the escalation was "very dangerous".
US National Security Council spokesman John Kirby said the Americans "certainly urge all sides to avoid further escalation" while supporting their ally Israel's right to defend itself.
Egypt has mediated in previous flare-ups in fighting between Gaza militants and Israel, including the 11-day war in May last year.
Israel's continuing assault is the most sustained since that conflict, which claimed 250 lives in Gaza and 13 in Israel.
The Israeli military routinely conducts strikes in response to occasional rocket fire from Gaza, particularly incidents involving groups its says are affiliated to the Hamas militant organisation that controls the Palestinian territory.