US Supreme Court Justice Antonin Scalia - one of the most conservative members of the high court - has died.
Justice Scalia, 79, was appointed by President Ronald Reagan in 1986.
He died in his sleep early on Saturday while in West Texas for hunting trip, the US Marshalls Service said.
Justice Scalia's death could shift the balance of power on the US high court, allowing President Barack Obama to add a fifth liberal justice to the bench.
The court's conservative 5-4 majority has recently stalled major efforts by the Obama administration on climate change and immigration.
"For almost 30 years, Justice Scalia was a larger-than-life presence on the bench," President Obama said, calling him "an extraordinary judicial thinker" with "an incisive wit".
The president said he intends to name a replacement in due time, despite calls from Republicans to wait until the next president is elected.
"There will be plenty of time for me to do so and for the Senate to fulfil its responsibility to give that person a fair hearing and a timely vote," Mr Obama said.
The death of Antonin Scalia has turned the US presidential race, and Washington politics, on its head.
The ability of a president to shape the Supreme Court for years if not decades has been an important consideration for many voters in US presidential campaigns - but it is usually an abstract concern. With the passing of conservative firebrand Scalia, that is no longer the case.
Republicans in the US Senate will do everything they can to prevent Barack Obama, who has less than 11 months left in his presidency, from naming a successor to a court that had been sharply divided between liberals and conservatives. If they succeed, then the historic nature of the current presidential campaign could not be clearer.
A Democratic victory in November means a court with a decidedly more liberal bent. If Republicans prevail they preserve their slender conservative majority on a court that regularly issues landmark decisions on issues like gay rights, immigration law, healthcare reform, campaign finance reform and civil liberties.
Even if Mr Obama gets a nominee confirmed, the power his successor will hold is now crystal clear. Three of the eight remaining justices are over the age of 70.
