Hillary Clinton has secured enough delegates to become the presumptive nominee for president of the U.S. Democratic Party, U.S. news media report.
The unofficial delegate count reported by U.S. media would put Clinton into a head-to-head race for the presidency with presumptive Republican nominee Donald Trump.
The reports come as President Barack Obama prepares to formally endorse her as the best candidate to succeed him.
Clinton secured the 2,383 delegates needed to become the Democrats' first female presidential nominee on June 6 after a decisive weekend victory in Puerto Rico's primary election and a burst of last-minute support from super delegates, NBC News and the Associated Press reported.
AP said Clinton won 1,812 pledged delegates in state primaries and caucuses and also is supported by 571 superdelegates, according to repeated AP polling of the Democratic Party's more than 700 superdelegates.
But Clinton's rival, Bernie Sanders, said it was premature to call the race and has vowed to take his fight for the nomination to the Democratic National Convention next month rather than concede to Clinton.
Clinton also demurred, saying she's "flattered" by the media crediting her already with victory, but she will focus for now on winning a raft of state primary elections set for June 7 in the Democratic strongholds of California and New Jersey, Montana, New Mexico, North Dakota, and South Dakota.
Polling stations have already opened in New Jersey.
"Let's finish this primary strong and head into the general election together," she tweeted.
Her campaign manager, Robby Mook, said the media call on Clinton was an "important milestone," however.
A Sanders campaign spokesman castigated what he called the media's "rush to judgment" and said it was wrong of the Associated Press and NBC News to count the votes of superdelegates before they cast ballots at the Democratic convention.
"Our goal is to get as many delegates as we possibly can and to make the case to super delegates that I believe the evidence is fairly strong that I am the strongest candidate," Sanders said.
While most delegates are awarded by popular votes in state-by-state primary elections, superdelegates consist mostly of party leaders and elected senators, members of Congress and governors, and can change their minds at any time.
For that reason, the Democratic National Committee has echoed the Sanders campaign, saying the superdelegates should not be counted until they vote at the convention in Philadelphia.
The White House said the announcement of Obama's endorsement will come within days, although not before the June 7 primary elections are held.
Obama spoke with Sanders by phone on June 5, but the White House did not disclose what they discussed.
With reporting by AP, dpa, AFP, and Reuters