The US will bolster its military presence in the Middle East with an additional 1,500 troops, Donald Trump has confirmed, amid heightened tensions with Iran.

The president told reporters on the White House lawn that the troops would have a “mostly protective” role.

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

The forces will number “roughly” 1,500 and will 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 will include protecting US forces already in the region and ensuring freedom of navigation, the notification said.

Patrick Shanahan
Patrick Shanahan (Andrew Harnik/AP)

Earlier this week, officials said Pentagon planners had outlined plans that could have sent up to 10,000 military reinforcements to the region. Acting defence secretary Patrick Shanahan later said planners had not settled on a figure.

Washington began reinforcing its presence in the Persian Gulf region this month in response to what it said was a threat from Iran.

The US 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 centre in Qatar.

There are about 5,200 troops in Iraq and 2,000 in Syria.

Earlier this month, the US sent thousands more into the region around Iran, including an aircraft carrier strike group, four bomber aircraft and fighter jets.