At the start of 2015, there were some half a million Yemenis displaced from their homes due to the ongoing conflict there. By December more than 2.3m Yemenis have been forced out according to the latest United Nations figures.

Many have fled their homes in the cities with the fiercest clashes, including the southern port city of Aden and Yemen's third-largest city of Taiz.

Across Yemen, more than 21m people are now in need of some form of humanitarian protection and assistance and the displaced are often the most vulnerable. Many have moved into abandoned school buildings, more than 3,000 of which, according to the UN, have been closed due to the violence, while others have sought refuge with relatives.

With displacement comes a whole range of concerns, for both hosting communities and the displaced. Resources, including access to water, food and sanitation, have been stretched to breaking point in often overcrowded shelters, increasing risk of disease and violence.

"I was displaced from al Jahmaliyya area that witnessed fierce clashes. We fled due to the shelling and shooting that continues to happen there. So I took my kids and came here," said Majed Mohammed, who is now living in an abandoned school in Taiz.

In the capital Sanaa, one resident describes his neighbourhood as a "ghost town" left in ruins from repeated airstrikes and clashes throughout the war.

"As you can see, there are lots of damaged homes around us and their residents have fled. Some have fled to the countryside, some have fled the country all together, and some have fled to other cities," said Sanaa resident Ali Ahmed al Nahari.

"This neighbourhood has become a town of ghosts. There is no one that can provide relief or record the damages or record anything," he said.

Yemen's warring sides are due to start peace talks in Geneva on 15 December, the most serious effort to end the civil war so far. The conflict between a Saudi-led Arab alliance and the Iranian-allied Houthis has outlasted two earlier UN attempts at peace making, caused one of the world's worst humanitarian crises and pushed Yemen towards total chaos.

Fuelling the urgency behind the talks is a perception in the West that the war, in part a proxy contest between rivals Saudi Arabia and Iran, is a dangerous distraction diverting regional attention from what should be the pre-eminent task of fighting Islamic state (Isis) on its home turf and ending Syria's larger war.

According to officials in the government of President Abd-Rabbu Mansour Hadi, Western countries are keen to avoid a power vacuum that could give jihadist militants the haven they now enjoy in the southern port of Aden and other lawless areas.

The newest branch of Isis (Daesh) has exploited the chaos to launch spectacular attacks in Yemen on both the Shi'ite mosques of the Houthis and senior officials and troops loyal to the government.