Israeli strikes on Saturday killed at least 48 people in the Gaza Strip, Palestinian health authorities said, as clashes took place in central and southern areas of the enclave ahead of the planned start of a polio vaccination campaign.

The United Nations is due to start vaccinating some 640,000 children in the territory against polio, relying on daily eight-hour pauses in fighting between Israeli forces and Hamas militants in specific areas of the besieged enclave.

On Saturday, medics administered vaccines on some of the children at Nasser Hospital wards in a symbolic move before the official campaign begins.

The campaign follows confirmation last week that a baby was partially paralysed by the type 2 polio virus, the first such case in the territory in 25 years.

WHO officials say at least 90% of the children need to be vaccinated twice with four weeks between doses for the campaign to succeed, but it faces huge challenges in Gaza, which has been largely destroyed by nearly 11 months of war.

On Saturday, as more than 2,000 medical and community workers prepared for the start of the campaign, medics in Nuseirat, one of the Gaza Strip’s eight historic refugee camps, medics said separate Israeli strikes killed at least 19 people, including nine members of the same family.

More than 30 other people were killed in a series of strikes in other areas of Gaza, medics said.

Residents and militant sources said fighters from Hamas, the Islamic Jihad, and other groups fought against Israeli forces in the northern Gaza Zeitoun neighborhood, where tanks have been operating for days, and in Rafah, near the border with Egypt.

The Israeli military said in a statement it continued to operate in the central and southern Gaza Strip. It said troops killed militants and dismantled military infrastructure in Gaza City, while they located weapons and killed gunmen in Tel Al-Sultan in western Rafah.

In Khan Younis, in the southern Gaza Strip, families returned to their areas after the army ended a 22-day offensive it said was aimed at preventing Hamas from regrouping. Footage showed large areas were flattened, and buildings and infrastructure were destroyed.

Medics said they recovered at least nine bodies from the area where the army operated.

The latest episode in the decades-old Israeli-Palestinian conflict was triggered on Oct. 7 when Hamas fighters attacked Israel, killing 1,200 and taking about 250 hostages, according to Israeli tallies.

Israel’s subsequent assault on the Hamas-governed enclave has since killed more than 40,600 Palestinians, according to the local health ministry. Nearly the entire Gaza population of 2.3 million has been displaced and the enclave has a hunger crisis. Israel faces genocide allegations at the World Court that it denies.

In the occupied West Bank, Israel forces pushed on with a military operation in the city of Jenin. Drones and helicopters circled overhead while the sound of sporadic firing could be heard in the city.