KHARTOUM, May 18 (Reuters) - About 18 people were killed and dozens wounded when Sudanese police clashed with refugees from southern Sudan in a camp near Khartoum on Wednesday, witnesses said.

"The troops, army and police, came in this morning and they shot at the civilians," said Majak Machar, a resident of the camp in Soba Aradi, about 30 km (19 miles) south of Khartoum.

"They wanted to take the people to another area and the people fought them because they didn't want to go."

Slums and camps surrounding the sprawling capital are home to more than 2 million people from all over Sudan. Most of them are southerners who fled two decades of civil war.

Machar, who was about 500 metres (600 yards) from the fighting, said police had killed seven or eight civilians and wounded dozens with live fire. They were also firing tear gas.

"The civilians then attacked the police and have killed at least two of them," he said. "They beat them with sticks," he said, adding that the fighting was continuing.

An interior ministry spokesman told Reuters at least 11 police had been killed.

One eyewitness said residents of Soba Aradi had burned down the local police station and killed the officer in charge, who was from the south of Sudan.

"The people said we will not go, we will die here in Soba Aradi," said Father Darwing, a local community leader. "They have been living there for 14 years," he said, adding that only police had been involved, not members of the army.

Witnesses said the displaced people had taken guns from the police and returned fire.

The governor of Khartoum declined immediate comment but was to hold a news conference later on Wednesday.

The United Nations said it had sent representatives to the area to try to calm the situation.

A U.N. official at the scene said hundreds of people were fleeing the area of the fighting.

The slum areas around Khartoum have little or no running water or electricity and aid agencies have found it difficult to fund improvements.

Khartoum authorities say they want to demolish the slums to relocate residents to permanent, planned housing plots.

But the United Nations has criticised the policy, saying the relocations have not been not carried out in consultation with the people being moved, and that were being taken to desert areas, long distances from the capital, where there are no services.