Unconfirmed reports 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.

President Hadi had previously taken refuge in Aden after the Houthis took full control of the capital Sanaa in January and placed him under house arrest.

The Houthis have said their aim is to replace President Hadi's government, which they accuse of being corrupt.

Gulf Arab states have accused Iran of backing the Houthis financially and militarily, though Iran has denied this.

The rebels are supported by army units loyal to the former president, Ali Abdullah Saleh.

Also on Thursday, local officials in the port city of Mukalla said Al-Qaeda militants had stormed a prison there and freed at least 150 detainees.

Officials said that among those freed was a senior figure in the regional wing of Al-Qaeda.