UNITED NATIONS -- Israel and Hamas have agreed to halt hostilities in the Gaza Strip for a World Health Organization (WHO)-led polio vaccination campaign, a WHO official said on Thursday.

Rik Peeperkorn, head of the WHO office for the West Bank and Gaza, told reporters in a video briefing that the UN health agency, the Hamas health ministry and the UN relief agency for Palestine refugees, known as UNRWA, would launch the campaign on Sunday.

He said the first two rounds of the vaccines would be administered from 6 a.m. to 3 p.m. local time in Gaza's central region for three days, followed by three days in the southern region and finally three days in the north. The pause in hostilities for each three-day campaign may be stretched to a fourth day if necessary.

The WHO official said 2,180 workers in 295 teams would administer the oral vaccines to 640,000 children under 10 years of age at 392 sites. The vaccine is to be delivered in two doses about four weeks apart.

Peeperkorn said if some children could not be brought into the planned 392 sites in hospitals and other medical points, "we will try to get to them."

After a 10-month-old girl was found to have contracted polio, partially paralyzing her left leg, the WHO announced plans for the Gaza vaccination campaign.

Also in Gaza, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said Israeli authorities announced that displaced people could return to specific areas in Deir al-Balah, the first time where return is officially allowed to an evacuated area.

OCHA said the evacuation orders are also severely constraining aid efforts. Recently, they have displaced many humanitarian colleagues and lost access to warehouses, water wells, other critical facilities and humanitarian routes.

"UN colleagues assessed the water, hygiene and sanitation conditions in two sites hosting over 1,200 families in Rafah," the office said. "People are struggling with drinking water as no trucking is currently available. They report skin diseases being the main morbidity among women and children, with no treatments available when they go to the medical points."

OCHA also said sea water floods the tents of those living directly on the beach in Mawassi.

In the West Bank, the office said there are reports of displaced families, particularly in urban areas where Israeli forces have repurposed homes as military positions. In multiple locations, military bulldozers have heavily damaged infrastructure and electricity and telecommunication outages continued.

"Military operations near hospitals also continue, effectively besieging these facilities and limiting the movement in and out, including that of medical staff," OCHA said.

The office said the UNRWA clinic in the Al Far'a refugee camp had to suspend operations on Wednesday, resuming on Thursday only when Israeli forces left the area. UN agencies warned of the risk of unexploded munition in some areas.