The US is sending a Patriot missile-defence system to the Middle East amid escalating tensions with Iran.
A warship, USS Arlington, with amphibious vehicles and aircraft on board, will also join the USS Abraham Lincoln strike group in the Gulf.
And US B-52 bombers have arrived at a base in Qatar, the Pentagon said.
The US said the moves were a response to a possible threat to US forces in the region by Iran, without specifying. Iran dismissed the claim as nonsense.
Tehran has described the deployments as “psychological warfare” aimed at intimidating the country.
Iran has also suggested it may resume uranium enrichment nuclear activities.
The Pentagon says US forces are responding to a possible threat to US forces, but did not offer any specifics regarding those threats.
The latest Pentagon statement on Friday said only that Washington was “ready to defend US forces and interests in the region”, adding that the US did not seek conflict with Iran.
There are about 5,200 US troops currently deployed in neighbouring Iraq.
The Patriot system can counter ballistic missiles, cruise missiles and advanced aircraft.
Officials told US media the USS Arlington had already been scheduled to go to the region, but its deployment was brought forward to provide enhanced command and control capabilities.
The USS Abraham Lincoln passed through the Suez Canal on Thursday, US Central Command said.
Iran’s semi-official Isna news agency quoted a senior Iranian cleric, Yousef Tabatabai-Nejad, as saying that the US military fleet could be “destroyed with one missile”.
Last year, US President Donald Trump unilaterally withdrew from a landmark nuclear deal America and other nations had agreed with Iran in 2015.
Under the accord, Iran had agreed to limit its sensitive nuclear activities and allow in international inspectors in return for sanctions relief.
