President Joe Biden spoke Thursday with Israeli Prime Minister Benjamin Netanyahu, a source familiar with the call told ABC News, their first conversation since seven World Central Kitchen aid workers were killed in an Israeli airstrike in Gaza.

       Biden had strongly condemned the incident, saying he was "outraged." He was expected to further express his anger and concerns about Monday's strike as part of a broader call with Netanyahu, who called the situation "tragic" and unintentional.

       World Central Kitchen has called for an independent investigation into the airstrike, during which its convoy was struck after leaving a warehouse in central Gaza. The organization said the vehicles were marked and their movements were coordinated with the Israel Defense Forces.

       MORE: World Central Kitchen calls for independent investigation into killing of aid workers in Gaza

       "This was a military attack that involved multiple strikes and targeted three WCK vehicles," the group said as it called on the U.S., Australia, Canada, Poland and the United Kingdom to join them in demanding a third-party probe into the events.

       A senior adviser for Netanyahu told ABC News claims by the aid group that the strike was intentional were "absurd."

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       Israeli Defense Minister Yoav Gallant told Defense Secretary Lloyd Austin on Thursday that a "thorough and transparent investigation is being conducted" and findings will be shared with partners, according to a readout of a call between the two leaders provided by Gallant's office.

       The last time Biden and Netanyahu spoke on the phone was March 18. Since then, tensions have continued to grow between the two leaders as they both face political pressures at home as the Israel-Hamas war stretches into its sixth month.

       Israeli Prime Minister Benjamin Netanyahu and President Joe Biden.

       AP/Reuters

       The IDF strike Monday that killed the WCK workers prompted Biden's harshest criticism yet of Israel's conduct as it goes after Hamas terrorists inside Gaza, saying the state hasn't done enough when it comes to deconfliction to allow humanitarian groups to deliver assistance to Palestinians.

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       "Incidents like yesterday's simply should not happen," Biden said in a statement Tuesday. "Israel has also not done enough to protect civilians."

       MORE: Palestinian doctor walked out of Biden meeting, underscoring tensions over war in Gaza

       However, despite the ramped-up rhetoric, administration officials have suggested overall strategy in U.S. support of Israel as it combats Hamas remains unchanged.

       "While we make no bones about the fact that we have certain issues about some of the way things are being done, we also make no bones about the fact that Israel is going to continue to have American support for the fight that they're in to eliminate the threat from Hamas," National Security Council spokesman John Kirby told reporters Wednesday.

       This is a developing story. Please check back for updates.