Two US Navy Seals who went missing during an operation to seize Iranian-made weapons - bound for Houthis in Yemen - are now presumed dead, the US military says.

The incident took place on 11 January when commandos were boarding a ship off the coast of Somalia.

According to media reports, one was swept away and the second jumped in after them, following protocol.

US Central Command said attempts are now being made to recover the bodies.

"We mourn the loss of our two Naval Special Warfare warriors, and we will forever honour their sacrifice and example," said the head of Central Command (Centcom), Gen Michael Erik Kurilla.

Air and naval units from the US, Japan and Spain spent 10 days searching an area of more than 21,000 sq miles (54,389 sq km) to try and find the commandos, with the help of oceanographers and meteorologists.

Navy Seals are members of a specialist maritime military force responsible for tasks including reconnaissance and carrying out covert operations.

Military officials told the Associated Press the first Seal was swept into heavy seas during the night mission as they were boarding an unflagged dhow - a traditional sailing ship - where the weapons were discovered.

The second then entered the water to try and save the first, as is taught during training.

US Secretary of Defence Lloyd Austin said "our hearts are with" the families of the "two brave Navy Seals".

"The entire Department is united in sorrow today. We are grateful to all who worked tirelessly to try to find and rescue them," he wrote on X.

Centcom said last week that warheads for Houthi medium range ballistic missiles and anti-ship cruise missiles, as well as parts for air defence systems, were among the items seized.

It added that initial analysis indicated the components were for missiles that have been used by the Iran-backed Houthis to target vessels travelling through the Red Sea recently.

The supply, sale and transfer of weapons to the Houthis is considered a violation of a 2015 United Nations Security Resolution, as well as international law.

Dozens of vessels have been targeted in the Houthi attacks, leading hundreds of cargo ships and tankers to be rerouted around the southern tip of Africa to avoid the strikes.

The Houthis, who support Hamas, say they are only targeting vessels with connections to Israel following the start of the war in Gaza. 

However, some of the ships they have hit have had no clear connection to Israel.

They have also begun attacking ships associated with the US and UK after both countries launched airstrikes against Houthi positions in Yemen in retaliation to the Red Sea attacks. The group controls the country's north, capital Sanaa and the Red Sea coastline.

Both the US and UK say they are not seeking a conflict with the Houthis but are trying to protect the international trade route.