The U.S. Navy has sent an aircraft carrier and a guided-missile cruiser toward Yemen.
The U.S. Navy sent the carrier USS Theodore Roosevelt and its escort cruiser, USS Normandy, from the Gulf into the Arabian Sea on April 19.
Army Colonel Steve Warren, a Pentagon spokesman, denied reports the ships were on a mission to intercept Iranian arms shipments to Yemen.
The ships will join seven other U.S. warships in the waters near Yemen, where Iranian-backed Huthi rebels are battling forces loyal to the Western-backed president.
The U.S. Navy said it had increased its presence in the area because of the instability.
It said in a statement the purpose was to "ensure the vital shipping lanes in the region remain open and safe."
The actions come as U.S. officials closely monitor a convoy of seven Iranian ships believed to be headed toward Yemen with unknown cargo aboard.
At the White House, spokesman Josh Earnest acknowledged concerns about arms shipments from Tehran to the Huthis.
"We have seen evidence that the Iranians are supplying weapons and other forms of support to the Huthis in Yemen," Earnest said.
"That's the kind of support that will only contribute to greater violence in that country, a country that's already been racked by too much violence."
The Shi'ite Muslim Huthi fighters control much of Yemen after seizing the capital Sanaa in September, 2014.
Saudi Arabia and a coalition of its Arab allies have launched air strikes in an effort to stop the advance of the Huthis, a move Tehran has condemned.
In a column published April 20 in the New York Times, Iranian Foreign Minister Mohammad Javad Zarif called for a regional dialogue, and said "Yemen would be a good place to start."
He noted that Iran had urged an immediate cease-fire, humanitarian aid, and an "intra-Yemeni dialogue" leading to the formation of a national unity government.
Reacting to Zarif's remarks, U.S. State Department spokeswoman Marie Harf said Washington might talk with Iran about promoting regional stability.
However, Harf noted there was a difference between talking with the Iranians and working with them.
"We've always said we won't be coordinating or working with the Iranians, and there's a difference between discussing and working with," she said.