UN Secretary-General Kofi Annan says Sudan's government has promised to "remove all obstacles" to easing the humanitarian crisis in Darfur.
Kofi Annan is in Sudan to highlight the urgency of the Darfur crisis
Mr Annan has just ended a tour of the region in which he visited refugees camps in Chad, neighbouring Darfur.
He called upon Sudan's government to disarm the Arab militias accused of terrorising the area's inhabitants.
But a spokeswoman for Human Rights Watch told the BBC Sudan's government "rarely ever" honours its promises.
"Their track record is very poor. They prefer to promise... and later go to do whatever they set out to do to begin with," Jemera Rone told the World Today programme.
The UN has warned tens of thousands of refugees could die from famine and disease unless allowed to return home.
The World Health Organisation said at least 10,000 refugees face death from diseases such as cholera, malaria and dysentery, as the rainy season arrives in July.
Some one million people have fled their homes in the Darfur region and at least 10,000 have already died in a conflict in which the Janjaweed Arab militia has been accused of "ethnic cleansing".
There is not enough food, water or medicine in the refugee camps
Separately, a 15 July date has been set for negotiations between the warring groups in the Darfur region, according to the president of the African Union, quoted by Agence France Presse.
Alpha Oumar Konare said talks between rebels and the Khartoum government would take place in the Ethiopian capital, Addis Ababa.
Mr Annan called for the Sudanese Prime Minister, Omar al-Bashir, to take swift action by disarming the Janjaweed and ensuring refugees can receive aid and return home.
"My message is simple," he said, "violence must stop."
He said Mr Bashir had promised to tackle the problem and would agree a joint statement with the UN, to be issued on Saturday.
Sudan's foreign minister has said some 6,000 soldiers and policemen will be despatched to improve security in Darfur but did not specify when this would happen.
The UN Secretary General has this week visiting some of the 120,000 who have fled Darfur for neighbouring Chad.
During this week's high-profile visits to Darfur by Mr Annan and US Secretary of State Colin Powell, the Sudan government promised to rein in the Janjaweed militias.
Mr Powell warned that the UN Security Council could act if the violence continued. He said the government must take action "within days or weeks".
Senior Sudanese officials have denied that the militia is being backed by the government.
Emergency United Nations Relief Coordinator Jan Egeland said that getting help to Darfur, an area the size of France with few roads and little infrastructure was "one of the biggest logistical nightmares in the history of humanitarian assistance".
"We've doubled our presence in Darfur over the last five weeks and we will double again in the next five weeks, but we still need to triple it," he said.
In Zam Zam camp near the North Darfur capital, El Fasher, Mr Annan sat in a circle with refugees, listening to them explain why they could not return to their homes.
"First the planes were flying over us and bombing us. Then the Janjaweed came," said Zahara, 20.
"They started to shoot and burn. They took all our belongings. They took men and slit their throats with swords. The women they took as concubines," she said.
Mr Annan promised that refugees would not be forced to return home.
However, when he visited another camp, Meshtel, he found that the 3,000 people had been moved on - after UN officials had visited the night before.
"Where are the people?" the New York Times quotes Mr Annan as asking.
Sudanese official Al Noor Muhammad Ibrahim said they had been moved because conditions there were so bad but denied it was an attempt to hide the truth from the UN chief.