Updated at 11 a.m. ET

Former Secretary of State Hillary Clinton will officially announce her intention to seek the 2016 Democratic nomination for president on Sunday afternoon, ending years of speculation over her plans to pursue the Oval Office, NPR has learned.

People familiar with the campaign plan say that Clinton, long presumed to be the Democratic front-runner even without a formal announcement, will make the announcement possibly via a video and social media, some sources suggest.

As The Wall Street Journal notes:

"So far, Mrs. Clinton faces scant competition for the Democratic nomination. Polls barely register former Maryland Gov. Martin O'Malley or former Virginia Sen. Jim Webb. One potential heavyweight — Vice President Joe Biden — has said he is considering a campaign but has taken few apparent steps to prepare for one."On Thursday, former Rhode Island Gov. Lincoln Chafee surprisingly joined the field, and offered a biting critique from the left of Mrs. Clinton's record on foreign policy. 'The biggest question will be: What exactly did you accomplish in your four years as secretary of state?' he said in an interview. 'There was a lot of dust in the air. Not many concrete accomplishments.' "

Announcing now gives an edge to Clinton, who lost a bitter contest to then-Sen. Barack Obama for her party's nomination in 2008. The head start would give her fundraising team more time to generate the hundreds of millions of dollars typically necessary to mount a successful presidential bid.

Following the Sunday announcement, Clinton is "expected to travel to the first-in-the-nation caucus state of Iowa early next week for campaign events. Democratic strategists and advisers spoke on condition of anonymity because Clinton has not yet finalized all aspects of her announcement plan," The Washington Post writes.

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