The US military will send an additional 1,000 troops to the Middle East as tensions build with Iran.
Acting Defence Secretary Patrick Shanahan said the deployment was in response to what he described as “hostile behaviour” by Iranian forces.
The US Navy also shared new images it says link Iran to attacks last week on two oil tankers in the Gulf of Oman.
Washington has accused Iran of blowing holes in the vessels with mines. Iran has denied the allegations.
Tensions were further fuelled on Monday when Iran said its stockpile of low-enriched uranium would next week exceed levels set under the 2015 nuclear agreement.
It recently stepped up production in response to the US tightening sanctions. The 2015 deal, from which the US has withdrawn, curbed Iran’s nuclear programme in exchange for the lifting of sanctions.
Meanwhile, on Monday night three rockets hit a military base housing US troops north of Baghdad, the Iraqi military said. The US said it was “indirect fire” and did not cause injuries.
No group has admitted responsibility for the attack, though it follows warnings by US officials of an increased threat to US interest in Iraq by Iran-backed militias.