United States President Joe Biden has said he is “outraged and heartbroken” by Israel’s killing of seven aid workers in Gaza, delivering some of his strongest criticism yet of the close US ally.

Biden’s rebuke is the latest example of his conflicting messages on the war, as his administration becomes increasingly critical of Prime Minister Benjamin Netanyahu’s government even while doubling down on the need to supply Israel with weaponry.In a statement issued by the White House on Tuesday night, Biden squarely accused Israel of not doing enough to protect innocent civilians in its war against Hamas.

“This conflict has been one of the worst in recent memory in terms of how many aid workers have been killed. This is a major reason why distributing humanitarian aid in Gaza has been so difficult – because Israel has not done enough to protect aid workers trying to deliver desperately needed help to civilians,” Biden said, describing the deceased aid workers as “brave and selfless”.Biden said an investigation that Israel has promised to carry out into the incident “must be swift, it must bring accountability, and its findings must be made public”.

“The United States will continue to do all we can to deliver humanitarian assistance to Palestinian civilians in Gaza, through all available means,” he said.The seven workers for the US-based aid organisation World Central Kitchen were killed on Monday night when the convoy they were travelling in was attacked after unloading food aid in central Gaza’s Deir el-Balah city.

A US-Canadian dual citizen, an Australian, a Pole, a Palestinian and three nationals of the United Kingdom were killed in the attack.

Netanyahu earlier on Tuesday acknowledged Israel’s responsibility for the attack, describing it as unintended and “tragic”.

“Unfortunately, in the past day, there was a tragic event in which our forces unintentionally harmed non-combatants in the Gaza Strip,” Netanyahu said in a video statement on Tuesday.

“This happens in war. We are conducting a thorough inquiry and are in contact with the governments. We will do everything to prevent a recurrence.”

Despite his insistence that Israel must protect civilians, Biden has continued to press for more weapons deliveries to Israel, including $18bn worth of F-15 fighter jets.

Since Hamas’s October 7 attacks on Israel, Biden has greenlit two emergency shipments of weapons to Israel worth more than $250m on top of a regular military aid allotment worth $3.8bn annually.

Biden’s handling of the war has generated increasing blowback from progressives, rights activists, Arab Americans and Muslims, raising fears for his bid for re-election in November within Democratic Party circles.