Dozens of unidentified troops have reportedly landed by sea in the Yemeni port city of Aden.
It comes as a Saudi Arabia-led operation against Shiite Houthi rebels continues.
The arrival of soldiers appears to be a last ditch effort by Riyadh and its Sunni allies to gain a foothold in Aden, after Houthi rebels swept into the centre.
The city has been the last major holdout of fighters loyal to the Saudi-backed President Abd Rabbu Mansour Hadi, who fled Aden last month.
Elsewhere in Yemen, suspected al Qaeda fighters have stormed a jail in Mukalla and freed 150 prisoners.
A Saudi border guard is also said to have been killed after coming under fire from the Yemen side.
The Houthis took over the capital Sanaa six months ago with supporters of former president Ali Abdullah Saleh and have continued to make advances. Iran is accused of backing the rebels, which it denies.