Biden said the safety of Americans is his "top priority" as president.
JERUSALEM -- President Joe Biden on Monday confirmed at least 11 Americans have been killed in the fighting in Israel, and believes more may have been taken hostage by Hamas.
"It's heart wrenching," Biden said in a statement. "These families have been torn apart by inexcusable hatred and violence."
Biden said his administration is aware other U.S. citizens are missing and that they are working with Israeli officials to learn more about their whereabouts, though he didn't elaborate on how many Americans are unaccounted for as the conflict rages.
"The safety of American citizens -- whether at home or abroad -- is my top priority as President," Biden said.
"While we are still working to confirm, we believe it is likely that American citizens may be among those being held by Hamas," he continued. "I have directed my team to work with their Israeli counterparts on every aspect of the hostage crisis, including sharing intelligence and deploying experts from across the United States government to consult with and advise Israeli counterparts on hostage recovery efforts."
President Biden had no public events on Monday, drawing criticism from some Republicans, although the White House said he was meeting with members of his administration and speaking with close allies.
Earlier in the day, Rep. Kevin McCarthy held a press conference to propose a "five-point plan" for how the U.S. should respond -- in which he said rescuing any American hostages should be the administration's "first priority."
"This administration must also make clear that harming any American will really result in the wrath of the United States," McCarthy said. "We cannot repeat what happened in Afghanistan. It must be clear that we do not negotiate with terrorists and no American will be left behind."
More than 900 people have died in and 2,500 injured in Israel since Saturday's surprise attacks from Hamas. Israeli Defense Forces previously said at least 100 people are missing, and on Monday Hamas threatened they will start killing hostages unless Israel stops shelling homes in Gaza without warning.
White House spokesman John Kirby, in an interview with ABC News Live Prime anchor Linsey Davis, said the administration has still not been able to confirm that Americans are among the hostages, but have remained in "constant touch" with Israeli officials in the last few hours.
"We don't really know whether they're just missing somewhere, or are lost, or whether they're being held hostage," Kirby said of the Americans whose whereabouts are unknown. "I think we have to accept the possibility that at least some of them are being held hostage by Hamas."
"We just don't have good, solid answers right now," he added.
Kirby, during an earlier appearance on CNN, became emotional when discussing the images of children kidnapped and young women abducted.
"Sorry, excuse me, it's very difficult to look at these images Jake and the human cost," Kirby said after choking up for several seconds. "And these are human beings, they're family members, they're friends, they're loved ones, cousins, brothers, sisters. Yeah, it's difficult."
The video in the player above is from an earlier report.