Austin said that munitions, air defence capabilities and other equipment and resources were "rapidly flowing" to Washington's closest Middle Eastern ally. Israel has vowed to crush Hamas, the Palestinian Islamist movement that rules Gaza.
"The U.S. Department of Defense stands fully ready to deploy additional assets if necessary," Austin told a news conference in Tel Aviv with his Israeli counterpart Yoav Gallant.
Israel launched its heaviest ever bombardment of the Gaza Strip after Hamas carried out an unprecedented and shock cross-border attack into southern Israel on Oct. 7.
Israel's response, which has already involved dropping thousands of bombs on Gaza, is expected to intensify as it prepares a possible ground assault on the narrow, densely populated coastal strip.
Austin cautioned that it was a time for "resolve" and not "revenge".
He added that the United States intended to stand alongside Israel in its war against Hamas at the same time as continuing to support Ukraine in its fight against Russia's invasion.
(Reporting by Ari Rabinovitch, Dan Williams, Henriette Chacar, John Davison; editing by Mark Heinrich)
