Sudan's security forces have again stormed a refugee camp in the troubled region of Darfur and attacked crowds.
An earlier police action in the camp was criticised by the UN
Police fired tear gas and assaulted residents at El-Geer camp near Nyala, hours before the UN's Sudan envoy was due to arrive, witnesses said.
The UN and African Union are seeing the assault as a calculated affront, says a BBC correspondent from the scene.
Sudan's ambassador in London played down the incident and said troops were trying to move people to a better camp.
Hassan Abedin said force was used only on a small number who were trying to incite resistance to being moved from the camp.
"Yes, I would say there were incidents of police... mishandling some individuals, but the idea is to enable the... vast majority of the people in this camp to move to a better camp," he told BBC News.
He denied Khartoum's policy in Darfur constituted genocide, and said the international community should await the outcome of a current UN probe into the allegation before jumping to conclusions.
Sudan has accused the international community of overplaying the security crisis in Darfur.
UN chief visits
UN Special Representative Jan Pronk arrived at El-Geer camp and visited a medical clinic in the area where the attack took place.
He has been travelling with the country's foreign minister.
Both listened to the testimony of women who were the victims of the assault.
Government officials in the area knew the UN secretary general's representative would shortly arrive at the camp, says BBC correspondent Fergal Keane.
In spite of this, government forces staged two assaults on displaced people and would not desist from bulldozing their camp, despite the presence of UN representatives, the African Union and international aid agencies.
At one stage, a plastic bullet was fired at a BBC cameraman standing next to a UN vehicle.
Tear gas was fired at people, mostly women and children, queuing at a nearby medical clinic.
Police action at the camp last week was condemned by UN Secretary General Kofi Annan.
A police commander at the scene told the BBC's correspondent that he was under orders to move the people to a new camp several kilometres away.
The UN has described the relocation programme as a breach of humanitarian law.
Some 1.6 million people have fled their homes and tens of thousands have lost their lives in the conflict in Darfur.
Pro-government Janjaweed militias are accused of driving the region's black Africans from their villages since two rebel groups began an uprising in February 2003.
In London, UK Prime Minister Tony Blair said the Sudanese government risked a "serious response" from the international community, if it reneged on agreements on Darfur.
"Time is running out for them to honour these commitments," he told parliament on Wednesday.
The raid took place a day after the government and the rebels signed what has been described as a breakthrough agreement aimed at ending the crisis.
At peace talks in Nigeria, sponsored by the African Union, the Sudanese government accepted a ban on military flights over Darfur.
A separate agreement covers humanitarian aid.
Talks aimed at finding a political solution to the conflict in Darfur are to resume in December.