The US Department of Justice reported that the country's prison population up to 30 June, 1998, had risen by 4.4% - or 76,700 inmates on the previous year.

In its regular report, the department's Bureau of Justice Statistics said the nation's incarceration rate had more than doubled over the last 12 years.

The national jail population was 41% white, 41% African American, 16% Hispanic with 2% coming from other backgrounds. Men accounted for 89% of the total prison population.

The trend towards more incarcerations began in the late 1980s.

Tough sentences

The report gave no reason for the increase, but experts have cited a number of factors, including tough new sentencing laws for violent criminals and more arrests for drug offences.

More criminals serving longer sentences led the prison population to surpass one million in 1990 and it has continued to rise.

The report's author, statistician Darrell Gilliard, said the prison population grew by an average 6.2% each year between the end of 1990 and mid 1998.

Although the growth rate was slower last year, Mr Gilliard said the difference was not statistically significant.

"The numbers have been pretty steady throughout the 1990s."

LA tops the prison league

The Justice Department's report said that prisoners in the custody of the states or the federal government accounted for two-thirds of the total while the rest - nearly 600,000 people - were held in local jails.

The largest jail populations were in Los Angeles, which had more than 21,000 inmates, New York City with nearly 17,700 inmates and Chicago with over 9,300 prisoners.

Jail authorities also supervised more than 72,000 men and women in the community under programmes such as electronic monitoring, home detention or work release, the report said.