President Donald Trump announced Friday that some 1,500 additional US troops would deploy to the Middle East against a backdrop of soaring tensions with Iran.

"We want to have protection in the Middle East," Trump told reporters as he prepared to set off on a trip to Japan.

"We're going to be sending a relatively small number of troops, mostly protective," Trump added. "It'll be about 1,500 people."

The deployment includes reconnaissance aircraft, fighter jets, engineers, and the extension of the presence of a Patriot missile defence battalion that accounts for 600 of the personnel.

"This is a prudent response to credible threats from Iran," said Acting Defense Secretary Patrick Shanahan.

Pentagon officials said the 1,500 additional troops were in response to recent incidents in the region that US intelligence had tied to Iran's leadership.

Those have included a rocket attack on the Green Zone in Baghdad, explosive devices that damaged four tankers in Fujairah at the entrance to the Gulf, and a Houthi drone attack against a Saudi oil installation.

"We view this as a campaign," said Rear Admiral Michael Gilday, director of the Pentagon's Joint Staff.

Gilday stressed that the expanded US military presence in the region, including an aircraft carrier task force, B-52 bombers, and an amphibious attack vessel deployed earlier this month, are defensive and meant to address an alleged ongoing threat from Iran.

"We think that through a combination of a very measured deployment of assets as well as public messaging, we are again trying to underscore that we are not seeking hostilities with Iran."