World Central Kitchen on Thursday demanded an independent investigation into the Israeli airstrikes that killed seven of its aid workers in Gaza as President Joe Biden was scheduled to speak to Prime Minister Benjamin Netanyahu by phone to express his anger over the deaths.

Chef Jose Andres, the founder of the global food charity, accused the Israeli military of "systematically" targeting the aid workers' convoy on Monday as they delivered much needed supplies to Palestinians in Gaza.

"This was a military attack that involved multiple strikes and targeted three WCK vehicles. All three vehicles were carrying civilians; they were marked as WCK vehicles; and their movements were in full compliance with Israeli authorities, who were aware of their itinerary, route, and humanitarian mission," WCK said in a statement.

"We have asked the governments of Australia, Canada, the United States of America, Poland, and the United Kingdom to join us in demanding an independent, third-party investigation into these attacks, including whether they were carried out intentionally or otherwise violated international law," the statement continued.

WCK said an independent investigation is the only way to "determine the truth of what happened," hold those responsible accountable and prevent such attacks from occurring in the future.

Biden, who has faced mounting criticism over his handling of the war and the escalating civilian death toll in Gaza, said he was "outraged and heartbroken" over the killings of the seven aid workers, calling their deaths a "tragedy."

The president said the deaths are not a "stand-alone incident," adding the war "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," he said in the statement released by the White House.

Netanyahu has been largely dismissive, saying only that the strike on the aid workers was "unintentional," and noting "this happens in war."

Defense Secretary Lloyd Austin also "expressed his outrage" over the killings to his Israeli counterpart, Yoav Gallant, in a phone call Wednesday.

The secretary "stressed the need to immediately take concrete steps to protect aid workers and Palestinian civilians in Gaza after repeated coordination failures with foreign aid groups," the Defense Department said in a readout of the call.

More than 33,000 people have been killed in the war, which began when Hamas militants attacked Israel on Oct. 7, Gaza's Health Ministry reported, according to the Associated Press. 

While the health ministry does not distinguish between civilians and combatants, it said women and children make up about two-thirds of those killed, the AP reported.