Former US Vice President Joe Biden has won the South Carolina primary, the latest contest in the race for the Democratic presidential nomination.
The victory, with support from African-American voters, was Mr Biden's first in the race and may give him momentum going into "Super Tuesday" next week, when 14 states go to the polls.
"Just days ago the press and the pundits had declared this candidacy dead," Mr Biden told hundreds of supporters at a victory rally in the South Carolina capital Columbia.
"You've launched our campaign on the path to defeating Donald Trump," he said.
"We have the option of winning big or losing big," Mr Biden added in a dig at Mr Sanders' prospects against Mr Trump in November's election.
With 99% of the ballots counted, Biden had 48.4% to 20% for Senator Sanders, a self-described "democratic socialist."
Billionaire activist Tom Steyer, who spent $23 million on advertising in South Carolina, was next with 11.4% but announced he was quitting the race even before the final results were published.
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Former South Bend, Indiana mayor Pete Buttigieg, who has been challenging Biden for the centrist vote, had 8% while Massachusetts Senator Elizabeth Warren had 7%.
A victory in South Carolina, where African-Americans make up around 60% of the Democratic primary electorate, was seen as crucial to Mr Biden's hopes of reviving his flagging campaign.
Mr Sanders has been the clear leader in the overall race, winning two of the first three contests and finishing in a virtual tie in Iowa with Mr Buttigieg.
South Carolina was seen as a key test of Sanders' support among African-Americans - crucial to a Democratic victory in November - but he only received the backing of around 15% of black voters while Mr Biden received 60% according to exit polls.
Mr Biden finished fourth in Iowa, fifth in New Hampshire and second in Nevada, and desperately needed a win in South Carolina ahead of Super Tuesday, which decides a third of the delegates who formally choose the Democratic nominee at the July party convention.
"The biggest question is whether this will slingshot Joe Biden into victory in some Super Tuesday states," said Larry Sabato, director of the Center for Politics at the University of Virginia.
Mr Sabato said Mr Biden's primary win - his first in three attempts at securing the Democratic presidential nomination - also increases the pressure on the other centrist candidates to leave the race.
Mr Buttigieg, Ms Warren, Minnesota Senator Amy Klobuchar and billionaire Michael Bloomberg have all made it clear they will stick around at least through Super Tuesday.
"Super Tuesday is three days away and we're looking forward to these big contests," Ms Warren, who has been challenging Mr Sanders for the progressive vote, told supporters at a campaign rally in Texas.
Mr Sanders congratulated Mr Biden on his victory at a campaign rally in Virginia but was confident of victory in the next primaries.
"The people on Super Tuesday and after are going to support this campaign," he said. "We are a movement of millions of people."
Mr Sanders also dismissed Democratic establishment fears that he would lose against Mr Trump, noting that dozens of polls have him beating the Republican incumbent.
Mr Trump also praised Mr Biden's victory and called on Mr Bloomberg to quit the race.
"Sleepy Joe Biden's victory in the South Carolina Democrat Primary should be the end of Mini Mike Bloomberg's Joke of a campaign," the president tweeted.
Sleepy Joe Biden's victory in the South Carolina Democrat Primary should be the end of Mini Mike Bloomberg’s Joke of a campaign. After the worst debate performance in the history of presidential debates, Mini Mike now has Biden split up his very few voters, taking many away!
— Donald J. Trump (@realDonaldTrump) March 1, 2020
The Bloomberg campaign, which has invested heavily in the Super Tuesday races, noted that the former New York mayor was not on the ballot in South Carolina.
Mr Biden, who served for eight years as vice president to Barack Obama, was the favourite in South Carolina, the first state with a substantial African-American electorate to hold a primary contest.
Mr Sanders, who narrowly lost the nomination to Hillary Clinton in 2016, is leading in nine of the 14 states to vote on Tuesday including California and Texas, the two biggest prizes.
