United States President Joe Biden said on Wednesday (May 8) he would stop US weapons supplies to Israel if it attacks Rafah in southern Gaza, his most direct warning to date over the prosecution of the war against Hamas.

In an interview with CNN, Biden also deplored the fact that civilians had been killed by the dropping of US bombs on the Palestinian territory.

His fresh warning came after the US last week halted a shipment of huge American bombs to Israel as it appeared ready to proceed with a major attack on Rafah – a city packed with Palestinian civilians sheltering near the Egyptian border.

"If they go into Rafah, I'm not supplying the weapons that have been used ... to deal with the cities," Biden said. "We're not gonna supply the weapons and the artillery shells that have been used."

Biden, a self-described Zionist, had long resisted stopping any of the US$3 billion in weapons the US sends each year to Israel – and pushed Congress for an increase in the wake of the Oct 7 attack by Hamas that triggered the major Israeli retaliation.

But US officials say privately that his hand was forced after Israeli Prime Minister Benjamin Netanyahu made clear he would go ahead with an assault on Rafah, defying Biden's public appeals to spare the city.

Under increasing pressure from the left of his own party to limit arms shipments, the Biden administration paused delivery last week of 1,800 907kg bombs and 1,700 226kg bombs.

"Civilians have been killed in Gaza as a consequence of those bombs," Biden said. "It's just wrong."

Biden may worry about alienating centrist voters if he shifts too far, while Netanyahu knows he needs US support at a time of wide global anger against Israel.

"We're not walking away from Israel's security," Biden insisted in the CNN interview. "We're walking away from Israel's ability to wage war in those areas."