* Highest forced displacement figure since WW2
* Guterres blames world powers inaction for "quantum leap"
* Syrians account for most of 2.5 mln new refugees
* 86 pct of refugees in developing world
By Stephanie Nebehay
GENEVA, June 20 (Reuters) - More than 50 million people were forcibly uprooted worldwide at the end of last year, the highest level since after World War Two, as people fled crises from Syria to South Sudan, the U.N. refugee agency said on Friday.
Half are children, many of them caught up in conflicts or persecution that world powers have been unable to prevent or end, UNHCR said in its annual Global Trends report.
"We are really facing a quantum leap, an enormous increase of forced displacement in our world," U.N. High Commissioner for Refugees Antonio Guterres told a news briefing.
The overall figure of 51.2 million displaced people soared by six million from a year earlier. They included 16.7 million refugees and 33.3 million displaced within their homelands, and 1.2 million asylum seekers whose applications were pending.
Syrians fleeing the escalating conflict accounted for most of the world's 2.5 million new refugees last year, UNHCR said.
In all, nearly 3 million Syrians have crossed into neighbouring Lebanon, Turkey, Iraq and Jordan, while another 6.5 million remain displaced within Syria's borders.
"We are seeing here the immense costs of not ending war, of failing to resolve or prevent conflict," Guterres said. "We see the Security Council paralysed in many crucial crises around the world."
NEW AND OLD CRISES
Conflicts that erupted this year in Central African Republic, Ukraine and Iraq are driving more families from their homes, he said, raising fears of a mass exodus of Iraqi refugees.
"A multiplication of new crises, and at the same time old crises that seem never to die," he added.
Afghan, Syrian and Somali nationals accounted for 53 percent of the 11.7 million refugees under UNHCR's responsibility. Five million Palestinians are looked after by a sister agency UNRWA.
Most refugees have found shelter in developing countries, contrary to the myth fuelled by some populist politicians in the West that their states were being flooded, Guterres said.
"Usually in the debate in the developed world, there is this idea that refugees are all fleeing north and that the objective is not exactly to find protection but to find a better life.
"The truth is that 86 percent of the world's refugees live in the developing world," he said.
Desperate refugees and migrants from the Middle East and Africa have drowned after taking rickety boats in North Africa to cross the Mediterranean to reach Europe, mainly via Italy.
Italy has a mission, known as Mare Nostrum or "Our Sea", which has rescued about 50,000 migrants already this year. Italy will ask the European Union next week to take over responsibility for rescuing migrants, a task that is costing its navy 9 million euros ($12.25 million) a month.
"It is important to have a European commitment there and to make sure that such an operation can be sustainable," said Guterres, a former prime minister of Portugal.
The EU bloc has harmonised its asylum system, but the 27 member states still differ in how they process refugees and in their approval rates for asylum applications, he said.
A record 25,300 unaccompanied children lodged asylum applications in 77 countries last year, according to UNHCR.
"We see a growing number of unaccompanied minors on all routes. We see them in the Mediterranean routes, we see them in the Caribbean route, through Mexico to the United States, we see them in the Afghan route into Iran, into Turkey, into Europe," Guterres said. "We see them everywhere." (Reporting by Stephanie Nebehay; Editing by Tom Heneghan)