"It is a very bad year for refugees worldwide. Now there are almost 10 million who have been expelled from their [countries] by insecurity, and that number is growing," Antonio Guterres said this week in Sudan.
In the latest available figures, UNHCR said the number of refugees under its mandate at the end of 2006 had grown 14 per cent from the previous year to 9.9 million.
The increase, the first since 2001, is largely because of the Iraq crisis, which has forced up to one-and-a-half million people to seek safety in other countries.
Iraqis now make up the second largest group under the UNHCR's mandate, with 1.5 million refugees.
The Sudanese make up the largest African refugee group, with more than 680,000 fleeing to other states largely because of the Darfur conflict.
Burundi and the Democratic Republic of the Congo also contributed to the rise.
But the two million Afghans living in other countries remain the largest group of refugees in the world.
Afghans: 2.1 million|
* The UNHCR figures do not include around 4.3 million Palestinian refugees in Jordan, Lebanon, Syria and the Palestinian Occupied Territories, who fall under the mandate of a separate agency
However the latest figures do not include the estimated 4.3 million Palestinian refugees in Jordan, Lebanon, Syria and the Occupied Territories.
"Let's be honest, in many cases their governments are part of the problem, and in many cases the international community does not have the capacity to help them," Guterres said.
"I have very grave concerns about the way things are moving ahead for refugees in many parts of the world."
Saftey concerns prevented Guterres from celebrating World Refugee Day in Somalia but he was keen to mark the occasion in south Sudan, where a reintegration programme of displaced people has been bucking the trend.
"This year we are supporting a huge reintegration of people to Sudan from many countries around the region - from Uganda and Ethiopia and Kenya and DRC," he said as he accompanied 161 refugees across the Ugandan border.
This year, UNHCR has already organised the repatriation of 35,000 people to Sudan, up from 20,996 last year.
"I hope [the model] of south Sudan can be established elsewhere - it is what we hope will happen in all the hotspots in the world," he said.