'We shall respond,' Biden says after three US troops killed

STORY: "We shall respond," he said at a campaign event in South Carolina, asking for a moment of silence.

Three U.S. service members were killed and dozens may be wounded after an unmanned aerial drone attack on U.S. forces stationed in northeastern Jordan near the Syrian border, Biden and U.S. officials said on Sunday.

Biden blamed Iran-backed groups for the attack, the first deadly strike against U.S. forces since the Israel-Hamas war erupted in October and sent shock waves throughout the Middle East.