WASHINGTON, Jan 12: The US Supreme Court ruled on Wednesday that the government may not indefinitely imprison immigrants who have been in the United States illegally for years and cannot be deported to their home countries.

The high court's 7-2 ruling was a defeat for the US Justice Department, which said the issue affected more than 2,000 detained immigrants who cannot be deported. Nearly half of them had arrived in the United States illegally from Cuba as part of the 1990 Mariel boatlift.

The court agreed to extend the reach of ruling issued in 2001 that limited detention to a "reasonable period," generally six months. That ruling concerned immigrants who entered the country legally, committed crimes that made them deportable, and then were refused re-entry by their home governments.

The latest decision involved immigrants in same circumstances, but who had entered the country illegally. The Department of Homeland Security's Bureau of Immigration and Customs Enforcement has reported that it has detained about 2,300 individuals who arrived at the border illegally and are awaiting deportation.

More than half of those being detained, including 920 who attempted to enter the United States illegally as part of the Mariel boatlift, have been imprisoned for more than six months while the government seeks to deport them.

Most of them had been in the country a number of years, committed a crime, served their sentence and then were taken into custody by immigration authorities. In the case of Daniel Benitez, who entered the United States illegally during the Mariel boatlift, his application to become a lawful permanent resident was denied after his conviction for a crime.

After serving a prison sentence for other crimes, Benitez in 2001 was returned to immigration custody while the United States sought to arrange his deportation to Cuba or another nation. In January 2002, Benitez sued and said he had been detained unlawfully.

The other case before the court involved another Mariel boatlift immigrant, Sergio Suarez Martinez. He was convicted of various crimes, released from prison and then taken into custody by immigration officials while awaiting deportation.

In the court's majority opinion, Justice Antonin Scalia rejected concerns by the government that the security of the US borders will be compromised if the immigrants must be released. If need be, Congress can act, he said.

Scalia said that after the 2001 ruling Congress adopted a law authorizing continued detention of certain immigrants, including those who present a national security threat or have been involved in terrorist activities. Chief Justice William Rehnquist and Justice Clarence Thomas dissented. -Reuters