The US Navy has sent an aircraft carrier and a guided-missile cruiser into the waters near Yemen, officials said on Monday, heightening the US maritime security presence as concerns mount over Yemen's escalating conflict.

The US Navy sent the carrier USS Theodore Roosevelt and its escort cruiser, USS Normandy, from the Gulf into the Arabian Sea on Sunday. 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 US warships in the waters near Yemen, which is torn by civil strife as Iranian-backed Houthi rebels battle forces loyal to the US-backed president.

The US 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 movements come as US officials closely monitor an approaching 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 Houthis.

"We have seen evidence that the Iranians are supplying weapons and other forms of support to the Houthis 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 Houthi fighters sidelined the central government after seizing the capital Sana'a in September and occupying a broad swath of Yemen, which borders oil giant Saudi Arabia.

Saudi Arabia and a coalition of its Arab allies have launched air strikes in an effort to stop the advance of the Houthis, a move Tehran has condemned.

One US official said the presence of the US warships off Yemen give American decision-makers options for action in the event the situation deteriorates.

The other US warships in the region include two destroyers, two mine-sweepers and three amphibious ships carrying 2,200 US Marines.

The United States has deepened intelligence cooperation with Saudi Arabia as it carries out airstrikes in Yemen and is providing logistical support to the Saudi-led coalition. But it is stopping short of directly participating in the strikes. – Reuters