NEW YORK - Duarnis Perez, a native of the Dominican Republic, became a U.S. citizen at 15 when his mother was naturalised. But he didn't know that meant he was also a citizen. He thought he was an illegal immigrant, and so did the authorities.

He was deported and subsequently arrested trying to sneak back into the U.S. from Canada. Perez spent almost five years in prison for unlawful reentry. But when he was released in 2004, an official of the U.S. Immigration and Customs Enforcement agency (ICE) reviewed his file and told him he had been a citizen all along.

The Perez case is one of a growing chamber of horrors coming under increasing scrutiny by Congress, the courts and civil liberties advocates.

ICE officials downplay the problem. "ICE does not detain United States citizens," said spokesman Richard Rocha, adding that agents thoroughly investigate people's claims of citizenship.

"ICE only processes an individual for removal when all available facts indicate that the person is an alien," he said.

Another case involved Majed Chehade, a 64-year-old German citizen whose wife, three children, and grandson are U.S. citizens.

Chehade owns a home in Massachusetts and is the export director of a German manufacturing company. He was on his way to visit his daughter in December 2006 when he was detained at Las Vegas Airport.

He was taken to a local jail, where he was subjected to strip and visual cavity searches, denied access to medical care and his prescription medications, and told that if he wanted to return to the U.S., he would have to spy on behalf of the government.

In that case, a federal judge rejected the government's request to have the case dismissed, finding that strip searches of immigrants arriving in the country, including those housed at local detention facilities, are constitutional only if supported by reasonable suspicion.

The court further held that the immigration agents' actions could be considered "extreme and outrageous conduct" and allowed an inquiry into the legality of the government's attempt to conscript a foreign national to spy to move forward.

Civil liberties organisations say these are not aberrations or isolated cases. They contend that they show a clear pattern of bureaucratic inefficiency, a lack of respect for the law, and the absence of clear guidelines for immigration officers.

Immigration authorities detain more than 300,000 men, women and children every year in a network of some 400 private facilities and state and local jails. Unlike other federal incarceration systems, there are no binding regulations that govern the conditions in those facilities.

Civil liberties advocates say the immigration detention system has caused an as-yet unknown number of deaths in recent years and subjected thousands of immigrants to inhumane conditions. A Washington Post investigation concluded that the system was "a hidden world of flawed medical judgments, faulty administrative practices, neglectful guards, ill-trained technicians, sloppy record-keeping, lost medical files and dangerous staff shortages."

And the New York Times editorialised, "For years, ICE has been allowed to create a makeshift system of immigration detention centers across the country with little to no oversight, and no mandate for accountability or transparency."

"The result: hundreds of thousands of immigrants each year are thrown into detention facilities where they live for weeks, months and in some cases even years on end with little contact with the outside world. They have no access to adequate medical care, even in the face of life or death emergencies."

The courts also continue to weigh in on the detention issue. In one recent case, a federal judge cited "persistent and widespread" problems in the federal immigrant detention system, and ordered the DHS to respond within 30 days to a petition by immigration detainees and civil rights groups that seeks to improve detention conditions at facilities across the country.

Last February, Department of Homeland Security (DHS) Secretary Janet Napolitano appointed Dora Schriro as a special advisor on ICE and detention and removal. The new position was created to focus exclusively on the significant growth in immigration detention over the last five years, and to focus on the arrest priorities at ICE.

In an April letter to Human Rights First, a legal advocacy group, Schriro said she was "dedicating these first months to the close examination of issues impacting detention and removal including arrest priorities, detention decisions and practices, and the utilization of alternatives to detention."

But rights groups say little has been heard from her since then.

According to the American Civil Liberties Union, "the federal government has failed to exercise meaningful oversight of immigration detention facilities nationwide."

The group said it "regularly receives complaints from immigration detainees whose cries for medical care go unanswered. All too often, the ACLU learns of detainees who have died from both serious diseases such as cancer and mundane conditions such as bacterial infections when earlier intervention could have made a difference."

The ACLU has filed a public records request asking the Barack Obama administration to make public changes it is making to a federal immigration enforcement programme that allows local police to arrest and process illegal immigrants.

And Amnesty International (AI) has recommended that "Detention should only be used in extraordinary circumstances, be justified in each individual case and be subject to judicial review."

Nevertheless, AI says that in the U.S., immigrants can be detained for months or years without a judicial warrant.

The detention and deportation issue is further complicated by immigration judges, many of who were political appointees during the George W. Bush administration and who have little or no experience in immigration law.

Most immigrants who appeal their cases to the Board of Immigration Appeals cannot afford lawyers, though reliable data concludes that legal representation significantly increases their chances of winning, especially in cases where the immigrant is seeking asylum in the U.S.

Addressing that issue, Attorney General Eric Holder has recently reversed a Bush-era order that said immigrants facing deportation do not have an automatic right to an effective lawyer. He said the government would appoint lawyers for immigrants contesting their deportation.

Meanwhile, ICE practices have also attracted the attention of Congress.

Congresswoman Lucille Roybal-Allard, a California Democrat - and the first woman of Mexican ancestry to be elected to the U.S. Congress - has introduced legislation to help to ensure that "detainees, especially unaccompanied children, are treated humanely, receive access to legal representation and obtain needed medical care."

Some civil liberties advocates see some modest glimmers of progress.

Francis A. Boyle, a law professor at the University of Illinois, told IPS, "It is extremely difficult to defend the basic human rights of undocumented aliens here in the United States. But there has been an amelioration of the mass raids of undocumented workers that Bush engaged in. Also, they have begun to put more pressure on employers, who are hiring these people illegally."

He added, "Obama should have reversed the Bush policy of giving local law enforcement agencies the power to police immigration law - something they are not qualified to do, which leads to racial profiling specifically against Latinos, and is counter-productive to ordinary policing of the community. But the Obama policies are certainly an advance for human rights over the racist, exploitative and near-totalitarian Bush policies."