A United Nations human rights official said he was barred from visiting an immigration detention center in New Jersey yesterday. It was the second time he was denied access to an American immigration jail on a weeklong monitoring tour.

The official, Jorge Bustamante, the United Nations special rapporteur on the human rights of migrants, said he was informed over the weekend that his visit to detained immigrants in the Monmouth County Correctional Institution in Freehold, scheduled for yesterday, had been canceled. Mr. Bustamante said he had received no explanation.

Mr. Bustamante was barred from a May 7 visit to the T. Don Hutto Family Detention Center in Taylor, Tex., where illegal immigrant families, including children, are held. Officials of Immigration and Customs Enforcement, the federal agency in charge of that center, said they canceled the visit because of a pending lawsuit over conditions there by the American Civil Liberties Union.

In a letter of protest yesterday to Zalmay Khalilzad, the United States ambassador to the United Nations, Mr. Bustamante said the State Department had approved his itinerary.