The return of millions of people to recovering nations such as Afghanistan, Angola and Sierra Leone has contributed to a sharp global decline in the number of refugees and asylum seekers over the past five years, but the sustainability of some of those returns remains a concern, according to a new report today by the Office of the U.N. High Commissioner for Refugees.

"The State of the World's Refugees: Human Displacement in the New Millennium," (Oxford University Press) was launched in London by High Commissioner for Refugees António Guterres and U.K. Secretary of State for International Development Hilary Benn. The book examines the changing dynamics of displacement over the past half decade. While the number of refugees – 9.2 million – is now the lowest in 25 years, it says the international system for dealing with human displacement has reached a critical juncture as it struggles with new challenges in an increasingly globalised world. These include the plight of tens of millions of internally displaced people; widespread confusion over migrants and refugees; tightened asylum policies and growing intolerance.

In his foreword to the book, Guterres notes that inter-state conflict is less prevalent today than internal strife and civil war, resulting in fewer refugees crossing international borders and more displaced within their own countries. Although the world's estimated 25 million internally displaced people do not fall under the 1951 Refugee Convention, they are nevertheless in urgent need of help.

"People who would otherwise seek safety in neighbouring states are more frequently compelled to remain within the borders of their own country, most often in similar conditions as refugees," writes Guterres, who says internal displacement is the international community's "biggest failure" in terms of humanitarian action. "Two long-running conflicts in Africa – the Democratic Republic of Congo and Sudan – alone accounted for an estimated 7.5 million internally displaced people in 2005."

The book notes, however, that the United Nations is beginning to make discernible progress toward helping the internally displaced, including a UN decision last year assigning sectoral responsibilities to specific agencies.

"UNHCR's role in the new division of labour is pivotal because it is focused on protection, the biggest gap in the system," the book says. "UNHCR is at a critical juncture in its 55-year history, having agreed to substantially expand its role to encompass the internally displaced. For the first time since the end of World War II, a comprehensive regime is being designed to address the needs of the forcibly displaced on both sides of the border."

Millions of refugees and asylum seekers have over the past five years benefited from international protection and from repatriation, integration in first-asylum states, or resettlement to third countries. More than 4 million have gone home to Afghanistan and hundreds of thousands more to Angola, Sierra Leone, Burundi and Liberia. South Sudan, struggling to emerge from two decades of civil war, could see more than 4 million internally displaced and refugees return in the next few years.

But ensuring that the uprooted can go home and stay home requires sustained international attention, from the return phase to reconstruction and long-term development. Bridging any gaps in that process is crucial in preventing such states from sliding back into another cycle of violence and displacement. Development plays a key role in ensuring that peace and economic recovery can take root.

The book also examines the plight of millions of refugees for whom no solutions are in sight. It says there are at least 33 such protracted refugee situations involving groups of at least 25,000 people who have been in exile for five years or more. Altogether, they accounted for 5.7 million of the world's 9.2 million refugees. "The majority of today's refugees have lived in exile for far too long, restricted to camps or eking out a meagre existence in urban centres throughout the developing world," the book says. "Most subsist in a state of limbo..."

In remarks prepared for Wednesday's book launch, Guterres cited the so-called asylum-migration nexus as one of the greatest challenges facing UNHCR today.

"In the past few years, asylum issues and refugee protection have become inextricably linked with the question of international migration, particularly irregular migration," he said. "Untangling the two means timely protection interventions to detect those in genuine need. UNHCR does not intend to become a migration agency. But migration requires our attention – to be vigilant of its effects on the right to asylum. While UNHCR recognizes it is the prerogative of states to control their borders and manage migration, such measures should not preclude the right of those in real need to adequate procedures in accordance with international law."

The number of international migrants has been estimated at more than 175 million, with asylum seekers and refugees comprising only a very small proportion, the book says. But the distinction between refugees, asylum seekers and migrants has been blurred and all are now seen in a negative light by some media and politicians.

"In public opinion, there has been a blurring of illegal migration and security problems with asylum and refugee issues," Guterres said. "This demonstrates the importance of combating intolerance and challenging the notion that refugees and asylum seekers are the agents of insecurity, rather than its victims."

UNHCR, which has twice won the Nobel Peace Prize, cares for some 19 million refugees and others of concern – including more than 5.5 million internally displaced – in over 116 countries.