GENEVA — United Nations rights experts said Friday they will not visit the Guantanamo Bay military prison because U.S. officials barred them from talking privately with detained terror suspects, making it impossible for the monitors to fairly assess the conditions there.

The United States had invited three experts appointed by the U.N. Human Rights Commission whose mandate is to check on rights abuses around the world.

"We deeply regret that the United States government did not accept the standard terms of reference for a credible, objective and fair assessment of the situation of the detainees at the Guantanamo Bay detention facility," the group said in a statement.

"These terms include the ability to conduct private interviews with detainees," they added.

"Under the circumstances, we will not be traveling to Guantanamo Bay Naval Station," the experts said, because doing so would "undermine the principles" of seeking to provide neutral, independent assessments of respect for human rights.

The United States holds about 500 prisoners at its Guantanamo Naval base in Cuba. They are accused of links to al-Qaida terror network or Afghanistan's ousted Taliban regime.

Most are held without charge or trial under the classification of enemy combatants, which the U.S. says does not accord them the same rights as prisoners of war under the Geneva Conventions.

U.N. experts have been trying to visit Guantanamo since 2002. Earlier this year, they said they wanted to go because they had reliable accounts that detainees have been tortured.

Many of these allegations had come to light through declassified U.S. government documents, they said.

The U.N. experts said they found it "particularly disappointing that the United States government, which has consistently declared its commitment to the principles of independence and objectivity of the fact-finding mechanisms, was not in a position to accept these terms."

U.S. officials in Geneva were not immediately available for comment.

U.S. officials so far have allowed only the International Committee of the Red Cross to visit detainees at Guantanamo, which began holding terror suspects in 2002.

The ICRC keeps its findings confidential, reporting them solely to the detaining power.

But some of the reports have been leaked by what the ICRC says were third parties.

The U.N. experts, however, would be expected to make a public report.

The human rights monitors are appointed to three-year terms by the 53-nation U.N. Human Rights Commission, the global body's top rights watchdog.

Their mandate covers rights abuses including torture, freedom of religion, health, independent judiciary and arbitrary detention.

They act independently and are not paid salaries by the U.N., which only covers their expenses.

The United States is a member of the commission and has generally accepted the work of the experts.

But Washington has criticized the commission in the past because it includes countries with poor human rights records.