The US military will send an additional 1,000 troops to the Middle East amid growing tensions 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 recent oil tanker attacks in the Gulf of Oman.
Iran announced on Monday it would no longer comply with part of the 2015 deal on curbing its nuclear ambitions.
It said it would exceed a limit agreed with international powers on its enriched uranium stockpiles by 27 June.
The images released by the Pentagon purport to show the remnants of an unexploded mine on the Japanese-owned Kokuka Courageous.
The photos appear to show it being removed by members of the Iranian Revolutionary Guard Corps and damage elsewhere to the tanker.
A Norwegian-owned vessel also reported being hit by blasts on Thursday.
Iran has denied involvement in the attacks and called US accusations “unfounded”.
In a statement on Monday, Mr Shanahan said the deployment of troops was in response to a request from US Central Command. He said the decision had been made in consultation with the White House.
The statement said the “United States does not seek conflict with Iran” but said the action was taken to “ensure the safety and welfare of our military personnel working throughout the region to protect our national interests”.
“We will continue to monitor the situation diligently and make adjustments to force levels as necessary given intelligence reporting and credible threats,” his statement went on.