ADEN (Reuters) - Dozens of unidentified troops landed by sea in Aden in an apparent last-ditch effort by a Saudi-led coalition to shore up a foothold in the southern Yemeni port city after Shi'ite Houthi fighters seized control of its centre on Thursday.
The soldiers arrived in a single vessel a few hours after the Iran-allied Houthis and their supporters swept into the heart of Aden despite an eight-day air campaign led by Riyadh to stem their advances.
The southern port city has been the last major holdout of fighters loyal to the Saudi-backed President Abedrabbo Mansour Hadi, who fled Aden a week ago and has watched from Riyadh as the vestiges of his authority have crumbled.
It was not immediately possible to verify the nationality of the troops, but the Saudi-led coalition says it is in control of the waters around Aden. If confirmed as a coalition move, it would be the first reported deployment of ground forces since Saudi Arabia launched the campaign a week ago.
The Houthis, who took over the capital Sanaa six months ago in alliance with supporters of former president Ali Abdullah Saleh, turned on Aden last month and have kept up their advances depite the Saudi-led intervention which aims to return Hadi to power.
Residents of Aden's central Crater district said Houthi fighters and their allies were in control of the neighbourhood by midday on Thursday, deploying tanks and foot patrols through its otherwise empty streets after heavy fighting in the morning.
It was the first time fighting on the ground had reached so deeply into central Aden. Crater is home to the local branch of Yemen's central bank and many commercial businesses.
"People are afraid and terrified by the bombardment," one resident, Farouq Abdu, told Reuters by telephone from Crater."No one is on the streets - it's like a curfew".
Another resident said Houthi snipers had deployed on the mountain overlooking Crater and were firing on the streets below. Several houses were on fire after being struck by rockets, and messages relayed on loudspeakers urged residents to move out to safer parts of the city, he said.
Hadi's rump government has appealed for international ground forces to halt the Houthis. Foreign Minister Reyad Yassin Abdulla said he could not confirm that coalition forces had landed in Aden, but told Reuters: "I hope so. I hope very much."
A Houthi spokesman said late on Wednesday that the fighting in Aden showed that Saudi Arabia's military intervention had failed. "The victories in Aden today embarrass this campaign and silenced the aggressor states," Mohammad Abdulsalam told the group's al-Maseera television.
The war on the Houthis is now the biggest of multiple conflicts being fought out in the Arabian Peninsula's poorest state, also grappling with a southern secessionist movement, tribal unrest and a powerful regional wing of Al-Qaeda.
The fighting has forced Washington to evacuate US personnel from the country, one of the main battlefields in the secret American drone war against al Qaeda.
Huge street demonstrations in 2011 linked to wider Arab uprisings forced veteran leader Saleh to step down, but he has re-emerged as an influential force by allying himself with the Houthis, his former enemies.
The Houthis are drawn from a Zaidi Shi'ite minority that ruled a thousand-year kingdom in northern Yemen until 1962. Saleh himself is a member of the sect but fought to crush the Houthis as president.
In the Arabian Sea port of Mukalla, 500 km east of Aden, suspected Al-Qaeda fighters stormed the central prison and freed 150 prisoners, some of them Al-Qaeda detainees, sources in the local police and administration said.
They named one of the escapees as Khaled Batarfi, a provincial Al-Qaeda leader who was arrested four years ago, security sources said. Soldiers loyal to Hadi clashed with the suspected Al-Qaeda fighters in Mukalla early on Thursday, residents said.
In Dhalea, 100 km north of Aden, where militia fighters from the south have battled Houthis for several days, residents said the militia were in control of the town but Houthis were sniping from rooftops.
Residents also reported air strikes overnight on the coastal town of Shaqra, which is under Houthi control and lies on the coast between Aden and Mukalla.