The United States vowed to take "all necessary actions" to defend American forces after a drone attack killed three U.S. troops in Jordan, while Qatar said it hoped U.S. retaliation would not damage regional security or undercut progress toward a new Gaza hostage-release deal.
Sunday's attack by Iran-backed militants was the first deadly strike against U.S. troops since the Israel-Hamas war erupted in October and marks a major escalation in tensions that have engulfed the Middle East.
White House National Security spokesman John Kirby said on Monday the United States did not want a wider war with Iran or in the region, "but we got to do what we have to do."
Iran has denied any role. Biden has previously ordered retaliatory attacks on Iran-backed groups but has so far stopped short of hitting Iran directly.
"Have no doubt - we will hold all those responsible to account at a time and in a manner of our choosing," Biden said on Sunday, while Austin said at the Pentagon on Monday:
"The president and I will not tolerate attacks on U.S. forces and we will take all necessary actions to defend the U.S. and our troops."
In Gaza, Israel launched an assault on the Hamas-ruled enclave's biggest city. Residents of Gaza City said air strikes killed and wounded many people, while tanks shelled eastern areas and naval vessels fired at western beachfront areas.
Israel said late last year it had largely completed operations in northern Gaza and has recently aimed the brunt of its might at southern Gaza. The renewed push in Gaza City, where residents reported fierce gun battles near the main Al-Shifa Hospital, suggested that the war was not going to plan.
