There has been widespread condemnation following a bomb attack on a hospital in Gaza in which 500 people are reported to have been killed.
Palestinian officials have placed the blame on Israel for Tuesday's attack.
Israel has claimed the Palestinian Islamic Jihad (PIJ) group was responsible for the blast on the Al Ahli al Arabi Hospital - an accusation the Islamist militant group denies.
The Israel Defence Forces (IDF) claimed the explosion was caused by a misfired Palestinian rocket which was aimed at Israel.
Palestinian President Mahmoud Abbas declared three days of mourning following the explosion, and cancelled a planned meeting with US President Joe Biden.
President Biden is visiting Israel on Wednesday, before travelling to Amman to meet the leaders of Jordan and Egypt.
WHO Health Emergencies Programme Executive Director Dr Mike Ryan has said any attack on health workers in this situation is a violation of international law.
"Any intentional attack like this, the word 'war crime' is a specific term that's attributed under law," he said.
"We as the WHO can't call it that; what we can say is that any attack on healthcare, any attack on health workers in this situation, is a violation of international law."
'The violence has to stop'
Speaking on Tuesday, Mr Ryan said finger-pointing is not helpful right now.
"The violence has to stop on all sides," he said.
"We have had this experience time and time again, where one side says they did it [and] the other side said they did it.
"Right now what matters is there are hundreds of dead people, hundreds if not thousands of more injured people.
"A hospital lost in its ability to serve its people; that's the reality, that's the brutal reality this evening," he added.
'Situation deteriorating rapidly'
UNICEF Ireland Executive Director Peter Power is calling for an immediate ceasefire and humanitarian access.
"The humanitarian situation in Gaza now is deteriorating rapidly now by the hour," he said.
"We're extremely concerned about the lack of access to water for over one million people, who have been displaced from Gaza City.
"What we need now is immediate humanitarian access to the Rafah Crossing on the southern border of Gaza with Egypt.
"We have them pre-positioned there - they're vitally needed for over one million people," he added.
On Tuesday, EU leaders held an extraordinary meeting of the European Council to discuss the conflict.
Extraordinary meeting of @EUCouncil on Israel and Palestine is underway. I’m dialling in from Government Buildings. At this deeply troubling moment, it’s vital for the leaders of the European Union to set out our common position and establish a unified course of action pic.twitter.com/Ey8FH1XoUI
— Leo Varadkar (@LeoVaradkar) October 17, 2023
Taoiseach Leo Varadkar said: "At this deeply troubling moment, it’s vital for the leaders of the European Union to set out our common position and establish a unified course of action."
Following the meeting, EU leaders once again condemned Hamas’ terrorist attacks against Israel and its population.
"The European Union condemns in the strongest possible terms Hamas and its brutal and indiscriminate terrorist attacks across Israel and deeply deplores the loss of lives. There is no justification for terror," the 27 members said in a statement.
They added that Israel has the right to defend itself "always in line with humanitarian and international law."
The members of the European Council also reiterated their call on on Hamas to immediately release all hostages without any precondition.
The EU said it is mobilised to ensure access to humanitarian assistance - access to water, electricity, food and medicine - for the populations most in need, in coordination with the United Nations.
