Representative Nancy Pelosi, former House speaker and a key ally of Joe Biden, signed a letter on Friday from dozens of congressional Democrats to the president and Secretary of State Antony Blinken, urging a halt to weapons transfers to Israel.
Support from Pelosi, a veteran member of Biden's Democratic Party, for stopping the transfer of weapons to Israel showed that the view is increasingly becoming mainstream in the party.
Friday's letter called on the Biden administration to conduct its own probe into an Israeli airstrike that killed seven staff of the aid group World Central Kitchen on Monday.
"In light of the recent strike against aid workers and the ever-worsening humanitarian crisis, we believe it is unjustifiable to approve these weapons transfers," the letter said.
It was signed by Pelosi and 36 other Democrats including Representatives Barbara Lee, Rashida Tlaib and Alexandria Ocasio-Cortez.
Punitive action taken by the IDF
The Israeli military said on Friday it dismissed two officers and formally reprimanded senior commanders after an inquiry into the aid workers' deaths found serious errors and breaches of procedure.
Biden held a call with Israeli Prime Minister Benjamin Netanyahu on Thursday in which he said Israel needed to do more to protect civilians or the US would change its policy.