"Like every nation in the world, Israel has the right to respond — indeed has a duty to respond — to these vicious attacks," Biden said at the White House.
At a highway rest stop near where Hamas gunmen killed Israelis and took hostages, Israeli volunteers are helping rescue civilians and support soldiers who are being dispatched to the front lines.
The group, founded in 1987, has vowed to annihilate Israel. Before this past weekend's attack, it was responsible for many suicide bombings and other deadly attacks on civilians and Israeli soldiers.
Israel's airstrikes continue on Gaza after Hamas militants made a surprise attack along Israel's southern border. Scores of Israeli hostages are being held captive in Gaza.
Sen. Cory Booker and Rep. Dan Goldman are back in the U.S. after sheltering in place as violence erupted in Israel on Saturday. Flight disruptions have left other U.S. citizens unable to get home.
The Israeli military said Sunday that it is still battling Hamas militants in several Israeli communities a day after they broke through the Gaza border to launch an unprecedented wave of attacks.