The US State Department issued a statement after two Israelis were killed when a gunman and two knife-wielding assailants attacked passengers on a Jerusalem bus.
In a separate incident, also in Jerusalem, another Israeli was killed when a Palestinian drove a car into a crowd at a bus stop then jumped out with a knife.
"The United States condemns in the strongest terms today's terrorist attacks against Israeli civilians," spokesman John Kirby said.
"We are in regular contact with the Israeli government and the Palestinian Authority," he added.
The attacks were only the latest in a two-week-old upsurge in violence that has raised fears of third full-scale Palestinian uprising, or "intifada."
After today's deaths, Israeli Prime Minister Benjamin Netanyahu warned that he would use "all means" at his disposal to restore order.