WASHINGTON (Reuters) - U.S. Defense Secretary Mark Esper said on Thursday there were indications Iran or forces it backs may be planning additional attacks, warning that the “game has changed” and it was possible the United States might have to take preemptive action to protect American lives.

U.S. Defense Secretary Mark Esper speaks about airstrikes by the U.S. military in Iraq and Syria, at the Mar-a-Lago resort in Palm Beach, Florida, U.S., December 29, 2019. REUTERS/Tom Brenner

“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, without providing evidence or details about the U.S. assessment.

“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 hurled rocks at the U.S. embassy in Baghdad during two days of protests, then 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.

Iran has rejected the accusation. Iranian Foreign Ministry spokesman Abbas Mousavi criticized American officials, in a statement, saying they have “the astounding audacity” to blame Iran for protests sparked by U.S. air strikes.

The unrest outside the U.S. embassy followed American strikes on Sunday against bases of the Tehran-backed Kataib Hezbollah group. Washington said the air strikes, which killed 25 people, were in retaliation for missile attacks that killed a U.S. contractor in northern Iraq last week.

On Wednesday, Supreme Leader Ayatollah Ali Khamenei condemned U.S. attacks on Iranian-allied militias in Iraq, blaming the United States for violence in Iran’s neighbor.

The protests marked a new turn in the shadow war between Washington and Tehran playing out across the Middle East.

“The game has changed and we are prepared to do what is necessary to defend our personnel and our interests and our partners in the region,” Esper said.

During the same press briefing, Chairman of the Joint Chiefs of Staff Mark Milley said there had been a sustained campaign by Kataib Hezbollah against U.S. personnel since at least October and the missile attack in northern Iraq was designed to kill.

“Thirty-one rockets aren’t designed as a warning shot, that is designed to inflict damage and kill,” Milley said.

He said it was highly unlikely anyone could overrun the U.S. embassy in Baghdad and if they did, they would run into a “buzzsaw.”

U.S. TROOPS PREPARED TO DEPLOY

The United States sent 750 troops to Kuwait this week and U.S. officials have told Reuters that about 3,000 additional troops could be sent to the region in the coming days.

Milley said additional troops had been alerted but a decision had not yet been made on deploying them. Since May, the United States has dispatched about 14,000 additional troops to the Middle East.

In his 2016 campaign, Trump promised to extract the United States from “endless wars.”

In a statement, Esper said the demonstrations outside the U.S. embassy in Baghdad were carried out by Iranian-backed Shi’ite militia, saying leaders were seen in the crowd and some members showed up wearing uniforms.

He said the series of rocket attacks on bases hosting U.S. forces in Iraq were being directed by the “Iranian regime” and specifically Iran’s Islamic Revolutionary Guard Corps leadership.

Earlier on Thursday, Revolutionary Guards Commander Brigadier General Hossein Salami said: “We are not leading the country to war, but we are not afraid of any war.”

The Iraqi government has attempted to integrate paramilitary organizations into its armed forces.

Esper said he had not seen the Iraqi government take sufficient action on stopping Iran-backed groups from carrying out attacks on U.S. forces and Baghdad needs to double down on efforts to control the groups.