The Krome detention centre in Florida holds 400 immigrants

Foreign nationals held in custody will now be given visiting rights and access to proper food medical care, recreation and libraries.

Immigrants are now the fastest-growing segment of the US prison population, largely because tough legislation passed in 1996 required the automatic detention and deportation of any immigrant with a criminal record, regardless of circumstances.

According to the INS about 250,000 people were deported last year. But critics say people coming from countries with no deportation agreement with the US, such as Cuba or Vietnam, are often confined indefinitely.

Enforcement problem

US detention centres currently house about 20,000 immigrants any given day, up from an average of 8,200 in 1997.

Under the new standards, immigration officials will have more discretion in deciding whether a detainee should be prosecuted or released.

From now on INS officials will be allowed to consider extenuating circumstances such as the type of crime committed and the person's length of stay in the country.

They also give detainees more rights, such as access to telephones, religious services, law libraries, typewriters and computers.

The guidelines are to be phased in this month at all detention centre administered by the INS, but it is expected to take longer for them to be implemented in state and local jails that also receive immigrants.

County jails in particular, and especially ones in Louisiana, Texas, New Jersey and Florida, have been criticised for alleged mistreatment of detained immigrants, including beatings, solitary confinement for trivial offences and inadequate water and food.

Critics say that conditions may not improve even after the standards are in place, because these could prove difficult to enforce.