“The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behavior by Iranian forces and their proxy groups that threaten United States personnel and interests across the region,” Shanahan said in a statement.
Reuters first reported plans to send U.S. additional troops to the Middle East earlier on Monday.
Fears of a confrontation between Iran and the United States have mounted since last Thursday when two oil tankers were attacked, more than a year after President Donald Trump announced Washington was withdrawing from a 2015 nuclear deal.
Iran said on Monday it would soon breach limits on how much enriched uranium it can stockpile under the deal, which a White House National Security Council spokesman said amounted to “nuclear blackmail.”
The 2015 accord, which Iran and the other signatories have maintained following Trump’s decision, caps Iran’s stock of low-enriched uranium at 300 kg enriched to 3.67 percent.
Reporting by Dubai newsroom and Parisa Hafezi in Dubai, Additional reporting by Bozorgmehr Sharafedin and William Schomberg in London, Francois Murphy in Vienna, Robin Emmott in Brussels, and Dan Williams in Jerusalem; Writing by Alistair Bell, Grant McCool; Editing by William Maclean, Cynthia Osterman and Sonya Hepinstall