Media playback is unsupported on your device Media caption Syria conflict: The refugees with 'nowhere to go'

The number of people living as refugees from war or persecution exceeded 50 million in 2013, for the first time since World War Two, the UN says.

The overall figure of 51.2 million is six million higher than the year before, a report by the UN refugee agency says.

Antonio Guterres, head of the UNHCR, told the BBC the rise was a "dramatic challenge" for aid organisations.

Conflicts in Syria, central Africa and South Sudan fuelled the sharp increase.

"Conflicts are multiplying, more and more," Mr Guterres said. "And at the same time old conflicts seem never to die."

Of particular concern are the estimated 6.3 million people who have been refugees for years, sometimes even decades.

Internally displaced

Media playback is unsupported on your device Media caption Antonio Guterres, UNHCR: "The world is becoming more violent"

People living in what the UN terms "protracted" refugee situations include more than 2.5 million Afghans. Afghanistan still accounts for the largest number of refugees overseen by the UNHCR (the five million Palestinian refugees come under UNRWA).

Neighbouring Pakistan is host to more refugees than any other country, with an estimated 1.6 million.

Around the world, thousands of refugees from almost forgotten crises have spent the best part of their lives in camps. Along Thailand's border with Burma, 120,000 people from Burma's Karen minority have lived in refugee camps for more than 20 years.

Refugees should not be forcibly returned, the UN says, and should not go back unless it is safe to do so, and they have homes to return to. For many - among them the more than 300,000 mainly Somali refugees in Kenya's Dadaab camp - that is a very distant prospect.

Some camps, the UN refugee agency admits, have become virtually permanent, with their own schools, hospitals, and businesses. But they are not, and can never be, home.

But the world's refugees are far outnumbered by the internally displaced (IDP) - people who have been forced to flee their homes, but remain inside their own countries.

Image copyright Reuters Image caption The UN says more people are displaced or are becoming refugees because the world is more violent

Media playback is unsupported on your device Media caption US Secretary of State John Kerry: ''We are talking about real people''

In Syria alone there are thought to be 6.5 million displaced people. The conflict has uprooted many families not once but several times. Their access to food, water, shelter and medical care is often extremely limited, and because they remain inside a conflict zone, it is hard for aid agencies to reach them.

Worldwide, the UN estimates there are now 33.3 million internally displaced people.

Human cost of war and persecution 51.2m people forcibly displaced worldwide 2.6m fled Afghanistan

1.6m refugees live in Pakistan

1.2m asylum claims worldwide GETTY

Large numbers of refugees and IDPs fleeing to new areas inevitably put a strain on resources, and can even destabilise a host country.

Throughout the Syrian crisis, Lebanon, Jordan and Turkey have kept their borders open. Lebanon now hosts more than a million Syrian refugees, meaning a quarter of its total population is Syrian. The pressure on housing, education and health is causing tensions in a country which itself has a recent history of conflict.

The UN is concerned that the burden of caring for refugees is increasingly falling on the countries with the least resources. Developing countries are host to 86% of the world's refugees, with wealthy countries caring for just 14%.

And despite the fears in Europe about growing numbers of asylum seekers and immigrants, that gap is growing. Ten years ago wealthy countries hosted 30% of refugees, and developing countries 70%.

Antonio Guterres believes Europe can and should do more.

"I think it's very important that Europe fully assumes its responsibilities," he said.

"I think it's also clear that we have in Europe good examples, Sweden, Germany, have taken very generous measures… but we need a joint expression of European solidarity."

Media playback is unsupported on your device Media caption Kim Ghattas reports on the "forgotten plight" of Afghan refugees

But what frustrates UN aid agencies most of all is being asked to cope with ever more refugees, while the UN's political arm, the Security Council, seems unable either to resolve conflicts, or to prevent them starting.

"The world is becoming more violent, and more people are being forced to flee," said Mr Guterres, adding that humanitarian organisations had neither the capacity nor the resources to cope.

"There is no humanitarian solution to these problems… to see the Security Council paralysed, when all these crises are evolving, is something that doesn't make sense."

"What frustrates me is the suffering of people, to see so many innocent people dying, so many innocent people fleeing, so many innocent people seeing their lives completely broken, and the world being unable to put an end to this nonsense."

Update 9 December 2014: This report has been amended to clarify that the five million Palestinian refugees come under the auspices of the United Nations Relief and Works Agency.