Hamas on Monday released two elderly Israeli women held hostage in Gaza as the United States expressed increasing concern that the escalating Israel-Hamas war will spark a wider conflict in the region, including attacks on American troops.

The death toll in Gaza rose rapidly as Israel ramped up airstrikes that flattened buildings in what it said was preparation for an eventual ground assault. The United States advised Israel to delay the expected invasion to allow time to negotiate the release of more hostages taken by Hamas during its brutal incursion two weeks ago.

A third small aid convoy from Egypt entered Gaza, where the population of 2.3 million has been running out of food, water and medicine under Israel’s sealed border. With Israel still barring entry of fuel, the U.N. said its distribution of aid would grind to a halt within days when it can no longer fuel its trucks. Gaza hospitals flooded by a constant stream of wounded are struggling to keep generators running to power lifesaving medical equipment and incubators for premature babies.

More than 1,400 people in Israel have been killed — mostly civilians slain during the initial Hamas attack. At least 222 people were captured and dragged back to Gaza, including foreigners, the military said Monday, updating a previous figure.

More than 5,000 Palestinians, including some 2,000 minors and around 1,100 women, have been killed, the Hamas-run Health Ministry said Monday

(With inputs from agencies)