NEW YORK –  Federal prosecutors say they can’t meet a judge’s demands they quickly deliver documents about thousands of immigrants who’ve been detained nationwide for months or years as their immigration statuses are reviewed.

The office of U.S. Attorney Preet Bharara laid out the government’s position to U.S. District Judge Richard M. Berman in a letter made public Wednesday.

The letter, dated Tuesday, came five days after the judge criticized the government, saying it had been on notice since the American Civil Liberties Union requested the documents nearly five years ago.

The ACLU eventually filed a Freedom of Information Act lawsuit in Manhattan federal court in 2011 seeking documents from the U.S. Department of Homeland Security and U.S. Immigration and Customs Enforcement.

The ACLU questioned the practice of “prolonged immigration detention — for months, if not years — without adequate procedures in place to determine whether their detention is justified.” It cited a dramatic increase in the number of immigration detainees in recent decades, noting they weren’t serving criminal sentences but were being detained by the thousands to ensure they’re available for removal from the country if removal is ordered and appeals are exhausted.

The judge said the government’s continued refusal to produce documents had stymied efforts to reform a system in which thousands of immigrant detainees, some applicants for asylum, languish in immigration jails longer than six months.

He also attacked as “painstaking and riddled with further delay” the government’s process for releasing documents, saying the government hasn’t produced any documents since his Sept. 9 order to release documents and had at times claimed it would take seven years to produce 100 files.

The government, though, said in its letter it is “not feasible” to produce documents from more than 22,000 individual files as ordered but said it can produce a reliable sample of 385 files within 15 months, with rolling releases within eight weeks of a revised order.

In 2009, The Associated Press conducted a computer analysis of an Immigration and Customs Enforcement database obtained under the Freedom of Information Act, finding there were 32,000 immigrants from 177 countries detained, including more than 18,000 with no criminal convictions.

The analysis showed that nearly 10,000 had been in custody more than a month, that 400 of those with no criminal records had been locked up more than a year, that a dozen had been held for three years or more and that one man from China had been incarcerated more than five years. Many of the longest-term non-criminal detainees were asylum seekers.

The analysis was referenced in the ACLU lawsuit.

According to a 2001 U.S. Supreme Court ruling, immigrants are supposed to be deported or released within about six months. The steady increase in the number of immigrants held behind bars grew considerably after Congress passed a pair of laws in 1996 requiring immigrants who committed crimes be locked up for deportation. The numbers continued to rise after the Sept. 11, 2001, terrorist attacks and amid anti-immigrant political rhetoric.