Justice Antonin Scalia, a towering conservative voice on the US Supreme Court, has died at the age of 79, triggering a political showdown over his succession in the run-up to the presidential election.
President Barack Obama ordered flags to fly at half-staff across the United States until the long-serving justice, first appointed by Ronald Reagan in 1986, is laid to rest.
Scalia's death after three decades on the Supreme Court bench has profound ramifications, and could potentially tip the balance of the highest court in the land from its current 5-4 conservative majority to a liberal one.
Obama led the chorus of tributes pouring in for the stalwart conservative, who died in his sleep at a private residence in the Big Bend area of West Texas, according to the US Marshals Service.
"For almost 30 years, Justice Antonin Scalia was a larger than life presence on the bench, a brilliant legal mind with an energetic style," Obama told reporters in Rancho Mirage, California.
"Tonight we honor his extraordinary service to our nation and remember one of the towering legal figures of our time."
Obama also spoke with Scalia's son Eugene "to pass along condolences to the entire Scalia family," the White House said.
But the US leader also fired the first shot in a tense battle over Scalia's succession.
Obama said he fully intended to nominate a successor, in accordance with his "constitutional responsibilities," after leading Republicans -- including all six conservative White House contenders -- argued that the outgoing president should not be allowed to fill Scalia's vacant seat.
He called for the Republican-controlled Senate to give his nominee a "fair hearing and a timely vote."
"These are responsibilities that I take seriously as should everyone," Obama said. "They're bigger than any one party. They are about our democracy."
The president nominates a Supreme Court candidate, who requires Senate approval before taking up the lifetime post.
For three decades, Scalia's outsized personality gave voice to the values of conservative America on the Supreme Court bench, on matters of religion, family, patriotism and law enforcement.
A staunch defender of gun rights and the death penalty, the Roman Catholic justice was also openly opposed to abortion, gay marriage and affirmative action.
The Supreme Court's conservative majority had recently stalled key efforts by Obama's administration on climate change and immigration, and replacing Scalia with a Democratic appointee could significantly alter the court balance.
Republicans immediately drew battles lines over the implications of the vacancy.