U.S. Defense Secretary Mark Esper said on Thursday that there were indications Iran or the forces it backs may be planning additional attacks and said it was possible the United States might have to take preemptive action to protect American lives."There are some indications out there that they may be planning additional attacks, that is nothing new ... we've seen this for two or three months now," Esper told reporters."If that happens then we will act and by the way, if we get word of attacks or some type indication, we will take preemptive action as well to protect American forces to protect American lives."Iranian-backed demonstrators who hurled rocks at the U.S. embassy in two days of protests withdrew on Wednesday after Washington dispatched extra troops.U.S. President Donald Trump, who faces a re-election campaign in 2020, accused Iran of orchestrating the violence. He threatened on Tuesday to retaliate against Iran but said later he did not want war.