The U.S. will bolster its military presence in the Middle East with an additional 1,500 troops, President Donald Trump said Friday amid heightened tensions with Iran.

Trump said the troops would have a "mostly protective" role as part of a build-up that began this month in response to what the U.S said was a threat from Iran without providing details or evidence.

"We are going to be sending a relatively small number of troops, mostly protective," the president told reporters at the White House before setting off on a trip to Japan. "Some very talented people are going to the Middle East right now and we'll see what happens."

Trump has in recent weeks alternated between tough talk toward Iran and a more conciliatory message, insisting he is open to negotiations with the Islamic Republic. He seemed to downplay the prospect of conflict when he spoke at the White House.

"Right now, I don't think Iran wants to fight and I certainly don't think they want to fight with us," he said.

The administration notified Congress earlier in the day about the troop plans.

The forces would number "roughly" 1,500 and would deploy in the coming weeks, "with their primary responsibilities and activities being defensive in nature," according to a copy of the notification obtained by The Associated Press.

Their mission would include protecting U.S. forces already in the region and ensuring freedom of navigation, the notification said.

Earlier this week, officials said Pentagon planners had outlined proposals that could have sent up to 10,000 military reinforcements to the region. Acting Defense Secretary Patrick Shanahan later said planners hadn't settled on a figure.

The U.S. has tens of thousands of troops in the Middle East, including at a major Navy base in Bahrain and an Air Force base and operations center in Qatar. There are about 5,200 troops in Iraq and 2,000 in Syria.

Earlier this month, the U.S. sent thousands more into the region around Iran, including an aircraft carrier strike group, four bomber aircraft and fighter jets in response to the unspecified threat.

Tension had been rising with Iran for more than a year. The Trump administration withdrew last year from the 2015 nuclear deal between the Islamic Republic and world powers and reinstated American sanctions that have badly damaged the Iranian economy.

The president has argued that the nuclear deal failed to sufficiently curb Iran's ability to develop nuclear weapons or halt its support for militias throughout the Middle East that the U.S. argues destabilize the region.