'An act of aggression'

United Arab Emirates (UAE) forces have occupied sea and airports on Yemen's remote island of Socotra, a day after deploying four military craft and more than 100 troops there, according to a Yemeni government official.

Condemning the move as an "act of aggression", the official said UAE soldiers also blocked Ahmed Obeid bin Daghr, Yemen's prime minister, and 10 ministers from leaving Socotra on Friday.

"The UAE has occupied the airport and seaport of Socotra island, despite the Yemeni government's presence there. What the UAE is doing in Socotra is an act of aggression," the official told Al Jazeera.

Saudi Arabia has pledged to send investigators to Socotra, according to the official.

Socotra, a UNESCO heritage site home to some 60,000 people, has a 3,000-metre-long runway, ideal for fighter jets and large military aircraft.

The UAE recently leased the island for 99 years and has confirmed carrying out military operations there.

Residents of the island said the flag of the UAE and images of Crown Prince Mohammed bin Zayed Al Nahyan, often known as MBZ, now adorn official buildings.

The deployment of Emirati troops on Thursday coincided with a rare visit to the strategically important island by Daghr.

Hundreds of islanders gathered to welcome him on Thursday.

They denounced UAE presence on the island and chanted slogans in support of President Abd-Rabbu Mansour Hadi and a unified Yemen.

Hadi's government and the UAE are formally allies in a war against Yemen's Houthi rebels.

A coalition led by Saudi Arabia has been battling the Iran-aligned armed group for three years to restore Hadi to power in the Arabian Peninsula country.

Relations between Hadi and the UAE has soured due to the latter's expanding influence in southern Yemen.

Hadi has previously accused the UAE of behaving like an occupier, according to the Middle East Eye website.

The UAE's move to exert control over Socotra is seen by many as the latest move by the Gulf state to spread its influence well beyond its borders.

The island is situated off the coast of Somaliland, where UAE has invested heavily in the commercial port of Berbera.

SECRET US MISSION IN YEMEN

According to a New York Times report, US deployed a team of special forces soldiers to Saudi Arabia's border with Yemen to help locate and destroy caches of ballistic missiles used by Houthi rebels to attack the Saudi capital, Riyadh.

The newspaper, citing unnamed US officials and European diplomats, said on Thursday that a team of about a dozen Green Berets were sent to the Saudi-Yemen border in December last year.

They arrived weeks after a ballistic missile from Yemen came close to Riyadh, according to the report.

As well as working with American intelligence analysts to help locate Houthi missile sites inside Yemen, the US special forces are training Saudi troops to secure their border, the Times reported.

It claimed the American soldiers are also working with surveillance aircraft to track Houthi weapons and their launch sites.

The New York Times called the troop deployment a "continuing escalation of America's secret wars", adding that the move contradicted US military's claim that its assistance to the Saudi Arabian-led coalition forces in Yemen is limited to "non-combat support".

Senator Tim Kaine, a Democrat senator, believed the mission was a "purposeful blurring of lines between train and equip missions and combat".

The Saudi-led coalition is battling Iran-backed Houthi rebels to restore the internationally recognised government of President Abd-Rabbu Mansour Hadi.

The war in Yemen has killed more than 10,000 people and displaced more than two million people.

The three-year civil war has contributed to a humanitarian catastrophe: about seven million people are on the brink of famine, while one million people are suspected to be infected with cholera.