A senior British aid official has been expelled from Chad while attempting to visit Darfur refugees still living in the east of the country.
Mukesh Kapila was the outspoken head of the UN in Sudan when the Darfur conflict began nine years ago.
Chad's interior minister personally ordered him to leave the country.
Mr Kapila says his expulsion is because Chad has close ties to Sudan's government, which he has accused of genocide.
This was Mr Kapila's first visit to the region since he was removed from his post in 2004 when - frustrated by his failure to persuade the international community to take action on the unfolding crisis in Darfur - he went public, speaking to the BBC.
Mr Kapila is haunted by his inability to stop the massacres in Darfur.
Some 2.7 million people have fled their homes since the conflict began in Sudan's arid western region, and the UN says about 300,000 have died - from war, hunger and disease.
Mr Kapila was in Chad to visit the refugee camps in the east of the country, where 200,000 people still live.
"I was frustrated, deeply saddened, and then very angry," he told the BBC when he learnt of his expulsion from the country.
Mr Kapila believes the reason is linked to the close political ties between N'Djamena and Khartoum.
"The fact that the Chadian authorities blocked me from seeing the Darfuri refugees, for which I had come to Chad, means that what I had said - warning the world of the Darfur genocide and blaming the Sudan government for it - still comes across the decade," he said.
"I guess that they were afraid that I would draw attention to the matter again."
The BBC was given access to the camps.
I found morale among people to be very low.
They face an uncertain future in the bleak surroundings of the Sahara desert, dependent on aid.
Couliboly Ouanna, from International Medical Corps, said that he was concerned that aid flows were drying up.
He said that although there are many children in the camp living in appalling conditions, it is difficult to arrange family planning. He cannot hand out condoms because he says people "want to replace the people who died in their country."
Aid organisations are cautious of making things better in the camps than in the sparsely populated villages around.
Where they can, they provide health care for Chadian locals as well as the refugees.
Some of the camps have an air of permanence.
Refugees live in mud houses, and health and education are no longer delivered from tents but from brick buildings.
Refugees grow their own crops which they sell in markets, along with meat from livestock which they breed.
There are 20,000 international peacekeeping troops in Darfur.
But while they may deter the worst atrocities, they have not brought stability and peace.
Continuing insecurity and a bad drought across the border have led to a new influx of refugees, who live on the margins of the existing camps in Chad.
Ishag Mekki, a Darfur refugee in Britain who campaigns for the region, said he fears that international pressure on the Sudan government has eased.
There has been speculation that Britain will forgive some debts of the Sudanese government, and he said that US President Barack Obama's administration cared less for the Darfur issue than President George Bush had done.
Mr Mekki says this has given the Sudan government a green light to launch a new campaign in South Kordofan - the region bordering South Sudan - using the same tactics that they used in Darfur nine years ago.
"People who were responsible are committing further crimes in South Kordofan, and still the international community is not fulfilling the fundamental UN resolutions to protect civilians," he said.
"I think that we were failed by the international community," he added.
Mr Kapila, now a special adviser to the Aegis Trust - a UK-based group that campaigns against war crimes - is concerned that the government in Sudan is being rewarded for allowing the south to secede peacefully.
He says no attempt has been made to arrest President Omar al-Bashir, the only head of state indicted as a war criminal, and the continuing conflict in Darfur risks being sidelined.