The fact-finding team was in the city of Port Harcourt, where the military dictatorship hanged the playwright Ken Saro-Wiwa and eight other Ogoni dissidents in November.
The minority Ogonis accused the regime of arresting 30 activists and detaining hundreds of people in advance of the UN visit. One Ogoni leader said he had received death threats. The government denied the reports and alleged the Ogonis were plotting to stir up trouble.
The four-man team, which has been in Nigeria for 11 days, was to meet with Saro-Wiwa's family and with families of the four Ogoni chiefs he was alleged to have murdered.
A letter to the UN team by Ledun Mitee, deputy president of the Movement for the Survival of the Ogoni People, said he had been threatened with death if he spoke to the team and hinted it should stay away.
"Before I am killed and another fact-finding team is arranged to probe the circumstances of my death . . . you may reconsider your planned visit to Ogoni," said the letter published in Lagos newspapers yesterday. "I do not want any more Ogoni to be harmed, molested or killed. We have had enough."
Mr Mitee said government agents had been going from village to village, rounding up anyone they suspected might provide the UN team with claims against the government.
The UN visit was prompted by the executions in November, which were carried out despite international appeals for clemency, and brought international condemnation.
Human rights groups maintain the nine were framed because of their opposition to the military ruler, General Sani Abacha, and to the oil industry. Oil brings in 90 per cent of Nigeria's export earnings, but has destroyed much of the water and farmland in the Ogoni region.
The UN team was given permission to visit several prominent political prisoners, including the jailed dissident Moshood Abiola, the presumed winner of the aborted 1993 presidential election, and the former military head of state, Gen Olusegun Obasanjo. They are among dozens of high-profile figures arrested since Gen Abacha took power in 1993.Reuse content