The United States is deploying an amphibious assault ship and a Patriot missile battery to bolster an aircraft carrier and B-52 bombers already sent to the Gulf.
In response to alleged threats from Iran, the USS Arlington, which transports marines, amphibious vehicles, conventional landing craft and rotary aircraft, and the Patriot air defense system will join the Abraham Lincoln carrier group, the Pentagon announced Friday.
USS Abraham Lincoln and accompanying ships have passed through the Suez Canal and are now in the Red Sea.
The carrier and a B-52 bomber task force were ordered towards the Gulf, as Washington reiterated that intelligence reports suggested Iran was planning some sort of attack in the region.
Officials had initially indicated that the military moves were based in part on indications that Iran had moved short-range ballistic missiles onto small boats called dhows along its shore.
Officials would not say if the intelligence showed that the boats have mobile launchers on them. But a notice to mariners in the region has warned of potential threats to commercial maritime traffic.
John Bolton, the national security adviser, announced the initial moves on Sunday, citing "troubling and escalatory indications and warnings" but did not explain what they were.
On Friday, a defense official said the Iranian threats also include potential attacks by Iranian proxies.
