A flotilla of nine Iranian naval and cargo ships that US officials feared was carrying arms to strife-torn Yemen sailed northeast in the direction of Iran on Friday, and this should ease US concerns, a Pentagon spokesman said.

The Iranian state news agency IRNA, however, quoted Iran's top navy commander, Admiral Habibollah Sayyari as saying on Saturday that the flotilla was still carrying out its mission in the Gulf of Aden.

Iranian-allied Houthi militia sidelined the Yemeni central government after seizing the capital Sanaa in September. The Shi'ite Muslim Houthis have advanced southwards since, capturing more territory and drawing Saudi-led air strikes.

On Friday, US Defense Secretary Ash Carter told a small group of journalists traveling with him after a trip to California: "The (Iranian) ships have turned around ... Obviously what their onward plans are, we don't know.

"It is a welcome event because it does contribute to de-escalation and that's what we're trying to suggest to all the parties there, is the best course, and those parties include the Iranians," Carter said.

Army Colonel Steve Warren, a Pentagon spokesman, said earlier the flotilla was in international waters about midway along the coast of Oman on Friday and still headed northeast.

Warren declined to say the ships were going back to Iran or headed toward Iran. Warren said the US military did not know their intent and the vessels could turn around at any point.

Iranian navy chief Sayyari told IRNA: "Currently the 34th fleet is located in the Gulf of Aden at the entrance to the Bab al-Mandab strait, and is conducting patrols" - a reference to two military ships that form part of the flotilla.

When the ships were first deployed earlier this month, Sayyari said that they were on a routine anti-piracy mission to protect shipping.

President Barack Obama said on Tuesday the US government had warned Iran not to send weapons to Yemen that could be used to threaten shipping traffic in the Gulf. Carter said on Wednesday the United States was concerned the ships might be carrying advanced weapons to Houthi rebels there.

The US Navy sent the USS Theodore Roosevelt and an escort warship into the Arabian Sea earlier this week to support seven US warships already in the area around the Gulf of Aden because of concerns about worsening chaos in Yemen.

A Saudi-led coalition, backed by the United States, began an air campaign last month to destroy heavy weapons controlled by Houthis that could threaten Saudi Arabia, the world's top oil exporter and arch-regional rival of Iran. The Saudis say their goal is to restore Yemeni President Abd-Rabbu Mansour Hadi.

Saudi Arabia said on Tuesday it was ending its campaign against the Houthis and shifting to a new phase of operations in Yemen. Bombing has resumed since then, however, and US officials have said the Saudis had indicated they would continue the air strikes as deemed necessary.-Reuters