President Biden said on Wednesday that he had told Prime Minister Benjamin Netanyahu of Israel that the United States would halt shipments of some weapons if the Israeli military invaded Rafah, the southernmost city in the Gaza Strip, using his strongest public language to date in his quest to deter a full-scale Israeli assault on the refugee-packed city.

“If they go into Rafah, I’m not going to be supplying the weapons that have been used historically to deal with Rafah, to deal with the cities, to deal with that problem,” Mr. Biden said in an interview with CNN’s Erin Burnett on Wednesday.

The interview was broadcast hours after Defense Secretary Lloyd J. Austin III acknowledged publicly that Mr. Biden’s decision last week to hold up delivery of thousands of heavy bombs was linked to Israel’s plans for a large offensive in Rafah, one of Hamas’s last bastions in Gaza, where more than a million Palestinians have taken refuge.

Israel and Hamas have been at war in Gaza since Oct. 7, when Hamas launched a devastating raid on Israel that left some 1,200 people dead, according to Israeli authorities. Mr. Biden has since struggled to both support Israel in the war on Hamas, and to press to limit civilian casualties. More than 34,000 people have been killed in Gaza, many of them women and children, according to the territory’s health authorities, and Mr. Biden’s pressure on Israel has grown as the numbers have risen.

But in recent days, Israel ordered the evacuation of 110,000 civilians in Rafah, conducted airstrikes against targets on the edges of the city, sent in tanks and seized the Rafah border crossing with Egypt.

In the interview, Mr. Biden also acknowledged in a way that he has rarely done that American bombs have killed innocent Palestinians. “Civilians have been killed in Gaza as a consequence of those bombs and other ways in which they go after population centers,” Mr. Biden said.

The president has objected to Israel’s planned Rafah operation out of fear that widespread civilian casualties could be caused by American bombs. He said on Wednesday that he would also block the delivery of artillery shells that could be fired into the urban neighborhoods of Rafah.

“I’ve made it clear to Bibi and the war cabinet, they’re not going to get our support if in fact they go on these population centers,” the president said, referring to Mr. Netanyahu by his nickname.

In the CNN interview, Mr. Biden said that he had warned Mr. Netanyahu against sending the Israeli military into civilian areas of Rafah. “It’s just wrong,” Mr. Biden said. “We’re not going to supply the weapons and artillery shells. I’ve made it clear to Bibi and the war cabinet that they’re not going to get our support if in fact they go into these population centers.”