By Imogen Foulkes
BBC News, Geneva
The head of the UN refugee agency has warned of a humanitarian catastrophe in the Sudanese province of Darfur if the security situation does not improve.
Millions have been displaced by the conflict in Darfur
Antonio Guterres called on Sudan's government to allow a UN peacekeeping force into the country, saying it was time to put the people of Darfur first.
Mr Guterres also warned that the escalating violence was now a threat to the stability of the entire region.
Three years of conflict have left millions displaced and thousands dead.
The UN says the situation shows no signs of improving, and aid agencies say it is getting worse.
Despite a peace deal signed in May between the government and one of the rebel groups, the violence is increasing.
Attacks on aid workers occur almost daily - 12 have been killed in the last three months.
Speaking in Geneva, Antonio Guterres, the head of UNHCR, said it was a situation which could not continue.
"I think we are facing a terrible disaster. War is starting again, violations of human rights are massive, situations of rape - these have all kinds of devastating forms of impact in the lives of this population and make us feel more and more uncomfortable because we are not able to help them.
"We cannot even have access to them. This is unacceptable, this has to stop."
Mr Guterres called on the government of Sudan to accept UN peacekeepers in Darfur.
Khartoum has so far rejected this, but Mr Guterres said the presence of UN troops was now urgently needed.
Aid agencies believe their work will be impossible without an international force in Darfur.
Privately many in the UN fear the escalating violence over the last few weeks is the build-up to a major attack by government forces.
If that happens, it could trigger another flood of refugees from Darfur into neighbouring Chad, where the UN refugee agency is already caring for 200,000 people.
Those camps are stretched to breaking point, Mr Guterres said, and a new refugee crisis along the borders could bring instability to the entire region.