U.S. Defense Secretary Lloyd Austin said Israel risked “strategic defeat” in its war with Hamas if it fails to heed warnings about the mounting civilian death toll.

“I have personally pushed Israeli leaders to avoid civilian casualties, and to shun irresponsible rhetoric, and to prevent violence by settlers in the West Bank,” Austin said Saturday in a speech to the Reagan National Defense Forum in Simi Valley, Calif.

Austin’s comments come as U.S. officials have grown increasingly vocal in their warnings to Israel about the death toll in the Gaza Strip. Those warnings, previously confined to closed-door meetings, have been thrust into the open by mounting pressure from Israel’s Arab neighbors, human rights activists and opinion at home — including the left of President Joe Biden’s Democratic Party.

While Austin and other U.S. leaders have vowed to continue supporting Israel, they worry that American support could become untenable if civilian casualties continue to mount.

During a trip to Israel this week, Secretary of State Antony Blinken said that the punishing campaign unleashed on northern Gaza shouldn’t be repeated as Israeli forces move south after the end of a multiday cease-fire with Hamas.

In California, Austin turned to personal combat experience to make his case.

“I learned a thing or two about urban warfare from my time fighting in Iraq,” he said. “Like Hamas, ISIS was deeply embedded in urban areas. And the international coalition against ISIS worked hard to protect civilians and create humanitarian corridors.”

“The lesson is not that you can win in urban warfare by protecting civilians. The lesson is that you can only win in urban warfare by protecting civilians,” he said. “In this kind of a fight, the center of gravity is the civilian population. And if you drive them into the arms of the enemy, you replace a tactical victory with a strategic defeat.”

Austin also reiterated U.S. advocacy for a two-state solution to the Israel-Palestine question.

“We believe that Israelis and Palestinians must find a way to share the land that they both call home,” he said. “It would compound this tragedy if all that awaited Israelis and Palestinians at the end of this awful war was more insecurity, more rage, and more despair.”

Israel and Hamas have been at war since Oct. 7, when the Iran-backed group’s fighters swarmed southern Israel, killing about 1,200 people and abducting 240. More than 15,000 people have been killed in Gaza since Israel started retaliatory airstrikes and a ground offensive, according to the health ministry in the Hamas-run enclave.

In the years before the Oct. 7 Hamas assault, successive U.S. administrations maintained a rhetorical commitment to a two-state solution, while putting a priority on normalization of relations between Israel and its Arab neighbors, most recently Saudi Arabia. The U.S. and the European Union have designated Hamas a terrorist group.

Austin also repeated warnings to Iran over attacks against U.S. personnel in Iraq and Syria by militias supported by Tehran. “We will not tolerate attacks on American personnel,” he said. “These attacks must stop.”

The U.S. defense chief cast the war in the Middle East as part of a growing constellation of national security concerns stretching from the Middle East to Eastern Europe and Asia.

“We’re living through challenging times,” Austin said.

“That includes the major conflicts facing our fellow democracies, Israel and Ukraine; bullying and coercion from an increasingly assertive China; and a worldwide battle between democracy and autocracy.”

He also warned that U.S. adversaries are increasingly finding common purpose in their desire to blunt U.S. power.

“From Russia to China, from Hamas to Iran, our rivals and foes want to divide and weaken the United States — and to split us off from our allies and partners,” he said.

Austin’s warnings about rising global threats were accompanied by a mention of the political challenges in Washington that risk stymieing the U.S. response.

“While I’ve got you here, let me urge you to pass a fullyear appropriation,” Austin told the multiple members of Congress assembled in Simi Valley, a reference to continued clashes over funding for the federal government.