An estimated 1.9 million people – more than 80% of the population – are estimated to have been displaced by the war, and some have had to flee as many as 10 times.

UN agencies and their partners are currently trying to stop the spread of polio in the overcrowded camps with poor sanitation where many of them are living.

The World Health Organization said the third phase of its vaccination campaign began in northern Gaza on Tuesday, after 446,000 children were inoculated in the centre and south earlier this month during localised pauses in the fighting agreed by Israel and Hamas.

On Monday, a team of 12 UN staff members on their way to the north to support the campaign was stopped by Israeli troops at a checkpoint for more than seven hours, according to UN Humanitarian Co-ordinator Muhannad Hadi.

“While at the checkpoint the team was informed that the IDF wanted to hold two of the UN staff members in the convoy for further questioning,” he said.

“The situation escalated quickly, with soldiers pointing their weapons directly towards the convoy personnel. Live shots were fired, and tanks and bulldozers approached, engaged with, and damaged UN vehicles, endangering the lives of UN staff inside the vehicles.”

The two staff were eventually questioned and then released following the intervention of senior UN officials to de-escalate the situation, he added.

The IDF said its forces had intelligence that a number of Palestinian suspects were present in the convoy, and that they delayed the convoy in order to question them.

Additional reporting by Thomas Mackintosh in London