A senior U.N. official expressed serious concern Tuesday over the erosion of human rights in the wake of the Sep. 11 terrorist attacks on the United States.

Mary Robinson, U.N. High Commissioner for Human Rights, told delegates that some countries -- which she refused to identify by name -- are introducing measures in apparent violation of core human rights safeguards.

Non-violent activities are being considered as terrorism in some countries while "excessive measures" are being taken to suppress or restrict individual rights, Robinson said. These restrictive measures cover rights to privacy, fair trial, asylum, political participation, freedom of expression, and peaceful assembly.

"We should be mindful of such fundamental principles as the presumption of innocence, non-discrimination and due process of law," she said.

Since Sept. 11, the United States has detained more than 1,000 people, largely Muslims or those of Middle Eastern origin, in its ongoing investigation of the terrorist attacks.

Several human rights organizations have complained that the government's refusal to disclose the identities of many of those detained, or to specify charges, is a violation of basic human rights.

The attacks apparently were masterminded by Saudi dissident Osama bin Laden while living in exile in Afghanistan. U.S. officials have said 19 hijackers, all of whom came from the Middle East, carried them out.

Last month, the U.S. Congress passed legislation giving sweeping powers to law enforcement officials, enabling them to conduct wire taps, intercept e-mail, and monitor phone conversations of suspected or potential terrorists.

Under the new law, immigrants also can be detained without charges - but not indefinitely.

The U.S. Senate voted 98 to 1 in favor of the anti-terrorist legislation while the House of Representatives voted 356 to 66.

Last month, U.S. President George W. Bush said his administration also plans to tighten immigration controls in order to keep potential terrorists from reaching the United States. The U.S. also will crack down on foreign students who overstay their visas.

"We plan on making sure that if a person has applied for a student visa, he actually goes to a college or university. And therefore, we are going to start asking a lot of questions that heretofore have not been asked," he said. The Canadian government has introduced similarly stringent legislation.

Under the new laws, police and immigration authorities will be given the power to compel testimony during investigations and nullify the right to remain silent to avoid self-incrimination.

The Canadian government also is tightening its asylum and refugee policies. Legal immigrants will be identified by a plastic card, which they will be expected to carry at all times.

Simon Potter, a vice president of the Canadian Bar Association, said the new laws are unprecedented in Canada.

"This new legislation has causes for concern," Potter said, "because of the definition of what terrorist activities are, the provision for preventative arrest, and the provision for forcing people to testify even if they don't want to."

"It is disturbing to think that the police can arrest you and keep you until they think you aren't going to be a menace any more," he added.

Robinson, who said all nations have contributed to common international human rights standards, urged governments Tuesday to "defend this common heritage."

"We should be careful to ensure that the right to privacy and the freedoms of expression, assembly and movement are not undermined," she added.

Robinson also decried the "worrying rise" in racial hatred following the Sep. 11 terrorist attacks. "This is an issue where real leadership is very much needed," she said.

She singled out Bush as being among world leaders who spoke out publicly against racial profiling of Muslims and Arabs following the terrorist attacks on New York and the Pentagon.

Robinson also said that governments, in their efforts to fight terrorism, must avoid turning innocent people into victims of counter-terrorism measures.

"This requires that government action in this area be guided by human rights principles", she stressed.

Human rights law wisely strikes a balance between the enjoyment of freedoms and the legitimate concerns for national security, she asserted, adding: "It requires that, in the exceptional circumstances, the principles of necessity and proportionality must be applied."