Unconfirmed reports, told BBC, have emerged of foreign troops landing in the Yemeni port city of Aden. It is not clear what nationality they are.
Aden has been the scene of fierce fighting as Houthi rebels have tried to advance on the heart of the city using tanks and armoured vehicles.
A Saudi-led coalition has staged seven nights of anti-rebel airstrikes.
Last week the rebels seemed close to taking Aden, forcing President Abdrabbuh Mansour Hadi to flee.
The Houthis have said their aim is to replace President Hadi’s government, which they accuse of being corrupt.
The rebels are supported by army units loyal to the former president, Ali Abdullah Saleh.