The World Health Organization has said it delivered 1.2m doses of polio vaccine to Gaza, with 400,000 more to follow, as part of an emergency campaign after the first case of the childhood disease in the war-hit coastal strip in quarter of a century.

The vaccinations, due to begin this weekend, will be accompanied by three-day pauses in the fighting in several areas of the territory to allow the inoculation of more than 640,000 children.

However, UN officials warned that Hamas and the Israeli military “must respect” the humanitarian pauses negotiated to allow the vaccinations, after two incidents this week – one deadly – when Israeli forces fired on aid vehicles, raising questions over how safely the vaccinations could be conducted.