The World Health Organization (WHO) said civilians and humanitarian aid workers should not be targeted, as Israel continued to bomb the Gaza Strip on Wednesday.

WHO chief Tedros Adhanom Ghebreyesus’ remarks came after the United Nations Relief and Works Agency for Palestine Refugees (UNRWA) said 11 staffers have been killed in Israeli airstrikes in the Gaza Strip since Saturday.

"Our heartfelt condolences to their families and the whole UNRWA team. WHO stands with you," said Tedros, noting he is devastated by the deaths of his UNRWA colleagues

"Civilians and humanitarians are not a target and must be protected at all times," he added.

Four more aid workers were killed after Israeli airstrikes hit the Palestinian Red Crescent headquarters in Gaza on Wednesday.

Israeli forces launched a sustained and forceful military campaign against the Gaza Strip in response to a military offensive by the Palestinian group Hamas in Israeli territories.

The conflict began Saturday when Hamas initiated Operation Al-Aqsa Flood against Israel – a multipronged surprise attack including a barrage of rocket launches and infiltrations into Israel via land, sea and air.

Hamas said the operation was in retaliation for the storming of the Al-Aqsa Mosque in occupied East Jerusalem and Israeli settlers’ growing violence against Palestinians.

The Israeli military launched Operation Swords of Iron against Hamas targets within the Gaza Strip in response.

That response has extended into cutting water and electricity supplies to Gaza, further worsening the living conditions in an area that has reeled under a crippling siege since 2007.