US President Joe Biden for the first time publicly vowed to withhold weapons from Israel if its forces make a major invasion of Rafah in southern Gaza while negotiations in Cairo on a ceasefire plan for the enclave were due to continue on Thursday, Reuters reports.

“I made it clear that if they go into Rafah … I’m not supplying the weapons,” Biden, whose administration has repeatedly asked Israel for its plan to protect civilians in Rafah, said on Wednesday in an interview with CNN.

Biden acknowledged that US bombs provided to Israel have killed Gaza civilians in the seven-month-old offensive aimed at annihilating Hamas.

Biden’s comments, his starkest to date, increase the pressure on Israel to refrain from a full-scale assault on Rafah, where hundreds of thousands of Palestinians have sought refuge after fleeing combat farther north in Gaza.

There was no immediate comment from Israel on Biden’s remarks, but Israeli Prime Minister Benjamin Netanyahu has said the Rafah operation would go ahead. Israel says it must hit Rafah to defeat thousands of Hamas fighters it says are there.