The seven victims, who were working for World Central Kitchen (WCK), were killed when their convoy was attacked from the air on Monday. Photo: BBC NEWS

Saying he was "outraged and heartbroken", he accused Israel of not doing enough to protect aid workers.

Israel promised an independent investigation after the UK, US, Canada, Australia and Poland lost nationals in Monday's attack.

Israeli President Isaac Herzog has apologised for the deaths.

The seven victims, who were working for World Central Kitchen (WCK), were killed when their convoy was attacked from the air on Monday.

Mr Biden called for Israel's investigation to be conducted swiftly, and said it "must bring accountability" and its findings be made public.

Distributing aid in Gaza had been "so difficult", he said, because Israel had "not done enough to protect aid workers trying to deliver desperately needed help to civilians".

In some of his strongest language since the war began, Mr Biden also accused Israel of not doing enough to protect Palestinian civilians.

"The United States has repeatedly urged Israel to deconflict their military operations against Hamas with humanitarian operations, in order to avoid civilian casualties," the US leader said.

In a video message, Israel Defense Forces (IDF) chief of general staff Herzi Halevi called the incident a "grave mistake" and said "it shouldn't have happened," blaming the strike on misidentification.

Humanitarian aid to Gaza is in doubt after WCK - a key provider of aid to the Strip - suspended operations.

Three of the killed aid workers were British nationals. A Polish national, an Australian, a Palestinian and a dual US-Canadian citizen were also killed. The IDF has promised an independent investigation into the incident.

UK Prime Minister Rishi Sunak spoke to Israeli Prime Minister Benjamin Netanyahu on Tuesday. On the call, he described the situation in Gaza as "increasingly intolerable" and "demanded a thorough and transparent independent investigation" into the killing of the aid workers.

Mr Sunak added that Israel needed to end restrictions on humanitarian aid and protect civilians, according to a Downing Street statement.