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 The 2015 deal, from which the US has withdrawn, curbed Iran’s nuclear programme in exchange for the lifting of sanctions.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.
The US troop deployment to the Middle East was announced by Mr Shanahan late on Monday.
In his statement, he said the “United States does not seek conflict with Iran” but the action was taken to “ensure the safety and welfare of our military personnel working throughout the region to protect our national interests”.
“The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behaviour by Iranian forces and their proxy groups that threaten United States personnel and interests across the region.”
He said the military would continue to monitor the situation and make adjustments to troop levels accordingly.
No details were given about where exactly the extra US forces would be posted.
Monday’s troop increase announcement comes on top of 1,500 extra announced by President Donald Trump last month.
Secretary of State Mike Pompeo said on Sunday that the US did not want war with Iran, but was nevertheless “considering a full range of options”.
He is due to meet the US military commander responsible for the Middle East at Central Command in Florida on Tuesday.