Major international aid groups warned Thursday it was now almost impossible to work in Gaza, as one accused countries supplying arms to Israel of being complicit in what "amounts to genocide".

Isabelle Defourny, president of Doctors Without Borders NGO, spoke out about the risk of genocide as 13 major humanitarian groups blasted Israel for restricting aid getting into the Gaza Strip. 

The killing of seven aid workers from the US-based World Central Kitchen (WCK) by Israeli air strikes Monday has sparked an outcry.

US President Joe Biden said he was "outraged and heartbroken" by the attack. 

But Defourny, president of MSF France, said the United States, Britain, France and other nations were "morally and politically complicit with what to our eyes amounts to genocide" by providing military support to Israel.

The aid groups also demanded that Israel abandon its plans to launch a ground offensive on Rafah in the south of Gaza, where well over one million civilians are sheltering. 

The bloodiest ever Gaza war erupted with Hamas's unprecedented October 7 attack which resulted in the deaths of about 1,170 Israelis and foreigners, most of them civilians,  according to an AFP tally of official Israeli figures.

Israel's retaliatory campaign, aimed at destroying Hamas, has killed at least 33,037 people, mostly women and children, according to the Gaza health ministry.

'Absolute horror'

While WCK has suspended its operations in Gaza, none of the 13 groups including Oxfam and Save the Children who made the joint call said they were pulling out.

Defourny, who said MSF had lost five of its 300 staff in Gaza, said the killing of the seven WCK employees was no surprise.

She said the "conditions today to deliver humanitarian assistance are not there (in Gaza).

"Because for the last six months we have witnessed the choices which Israel makes in waging war on an entire population, a population that is trapped, deprived of food and massively bombed. 

"Gaza is progressively being made unfit for human life," she added, it "has passed the threshold of absolute horror".

Defourny said the International Court of Justice ordered "measures to prevent a genocide" in January and again last week. 

But "Israel has so far done the exact opposite, continuing to block humanitarian aid and destroy vital civilian infrastructure as illustrated by the attack on WCK and the Al-Shifa hospital destruction", she added.

Israel has fiercely pushed back against accusations it is blocking aid, alleging instead that humanitarian groups have failed to distribute it. 

In war-torn Gaza, where vast areas have been reduced to rubble, 2.4 million Palestinians have been under bombardment for six months while enduring dire shortages of food, water, fuel and other basic supplies.

After the ICJ's January ruling, Israeli Prime Minister Benjamin Netanyahu said the charge against Israel "is not only false, it's outrageous, and decent people everywhere should reject it".

'War against civilians'

The charity Oxfam said that people in starving northern Gaza have been forced to survive on an average of 245 calories a day — less than a can of beans, and a fraction of the recommended average daily 2,100 calorie intake per person.

Scott Paul of Oxfam said almost half of people in the north are actually "living on less". 

"Is it any wonder that there is either an imminent famine or a famine that is actually taking place" there, he added.

The charities called for an immediate ceasefire, saying Israel and the countries supplying it with arms "have the obligation (in international law) to protect populations from atrocity crimes". 

Doctor Tanya Haj-Hassan, an American paediatric intensive care doctor, who has been working in Gaza hospitals, said "everybody's a target" in Gaza.

"Evidence on the ground does not suggest that this is a war against Hamas, but a war against civilians. 

"When you are in the operating theatre, you do not see Hamas, you see entire families wiped off the civil registry. 

"I saw (in theatre) direct sniper shooting of children in the head and elderly people."

She said she noticed a "consistent pattern of targeting particular groups (by Israeli forces) — health care workers, press and humanitarian aid workers."