President Joe Biden confirmed Tuesday that at least 14 Americans had been killed in a series of bloody attacks on Israel by Hamas over the weekend, adding that an unspecified number of American citizens were also believed to be among those taken captive by the militant group. In remarks from the White House on Tuesday, Biden also impassionately affirmed the United States’ alliance with Israel, condemning the incursions as “sheer evil.” “In this moment, we must be crystal clear: We stand with Israel. We stand with Israel,” he said. National Security Adviser Jake Sullivan said after Biden’s speech that he could not confirm the exact number of American hostages in Gaza, but said that there were at least 20 citizens missing. “We will work hour-by-hour both to determine whether we can account for any of those Americans, or to confirm exactly the number of Americans held hostage,” Sullivan said.