US Supreme Court Justice John Paul Stevens to retire
US President Barack Obama: Justice Stevens "at the top of his game"
Justice John Paul Stevens, the oldest member of the US Supreme Court, has announced he is to retire.
Justice Stevens leads the court's liberal bloc. His replacement will be nominated by President Barack Obama.
The judge, who turns 90 in 11 days time, says he will step down when the court finishes its work for the summer - in late June or early July.
Mr Obama hailed Justice Stevens as a "brilliant" jurist and said he would quickly nominate a successor.
His announcement has not come as a surprise, says the BBC's Steve Kingstone, in Washington.
"We cannot replace Justice Stevens's experience or wisdom," Mr Obama said at the White House.
JUSTICE JOHN PAUL STEVENS
Born 20 April 1920
Appointed to Supreme Court by Republican President Gerald Ford in 1975
Sided with liberal justices on cases involving abortion, civil rights and church-state relations
Led dissenting justices in case that sealed George W Bush's 2000 presidential election win over Al Gore
"I'll seek someone in the coming weeks with similar qualities: an independent mind, a record of excellence and integrity, a fierce dedication to the rule of law and a keen understanding of how the law affects the daily lives of the American people," he said.
Chief Justice John Roberts said in a written statement that Justice Stevens had earned the gratitude and admiration of the American people.
"He has enriched the lives of everyone at the court through his intellect, independence, and warm grace," he said.
Supreme Court justices serve for life and the US constitution gives the president sole authority to nominate them.
Nominations must be confirmed by the Senate. The nomination is likely to become a political battleground ahead of the Congressional mid-term elections in November.
Justice Stevens's polite, dignified interventions made him a likeable figure on the bench, but he was also a powerful intellectual and strategic presence, our correspondent adds.
He informed Mr Obama of his pending retirement in a one-paragraph letter addressed to "My dear Mr President".
Solicitor General Elena Kagan is seen as a possible successor
Analysts say Justice Stevens's departure will not change the court's conservative-liberal split because President Obama is certain to name a liberal-leaning replacement.
The Washington Post, quoting aides and Democrats close to the process, named three people as likely candidates to replace Justice Stevens - Solicitor General Elena Kagan and federal judges Diane Wood and Merrick Garland.
An administration official said Mr Obama was considering about 10 potential candidates for the post, Reuters news agency reported.
It will be the second time in his presidency that Mr Obama makes such a nomination. Last year he named Sonia Sotomayor to replace retiring Justice David Souter.
Justice Stevens was nominated in 1975 by then US President Gerald Ford, to replace Justice William Douglas, who had retired.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.