(The Center Square) – Democrat Joe Biden declared victory Saturday in his race to win the White House after several national news outlets called him the winner over President Donald Trump.

"America, I’m honored that you have chosen me to lead our great country," Biden said on his Twitter account. "The work ahead of us will be hard, but I promise you this: I will be a President for all Americans – whether you voted for me or not. I will keep the faith that you have placed in me."

Biden's Twitter account bio was edited to call him "President-Elect."

Biden's running mate, U.S. Sen. Kamala Harris of California, posted a video of her phone call with Biden: "We did it, Joe. You're going to be the next president of the United States.

Trump has not conceded, and a statement from the White House said the race isn't over.

"We all know why Joe Biden is rushing to falsely pose as the winner, and why his media allies are crying so hard to help him: they don't want the truth to be exposed," the statement began. "The simple fact is this election is far from over. Joe Biden has not been certified as the winner of any states, let alone any of the highly contested states headed for mandatory recounts, or states where our campaign has valid and legitimate legal challenges that could determine the ultimate victor."

NBC News, CNN, Fox News, The Associated Press and others gave Biden the win Saturday in Pennsylvania, where the former vice president was born. Pennsylvania's 20 electoral college votes would give Biden 273 in total by NBC and CNN's unofficial counts, and 284 by AP and Fox's counts; 270 are needed to win the presidency. The AP and Fox News called Arizona for Biden on Wednesday while CNN and NBC have not as votes continue to be counted there.

Biden would be the 46th president of the United States.

Trump is mounting a number of legal challenges in battleground states, including Pennsylvania, Nevada and Michigan.

Trump's legal team held a news conference Saturday in Philadelphia shortly after the race was called, claiming widespread voter fraud.

Trump attorney Rudy Giuliani said at the news conference that a number of lawsuits will be filed Monday in states across the country challenging counting methods, including . Giuliani said Trump would not concede when hundreds of thousands of ballots are in question in Pennsylvania alone.

With 98% of the vote counted in Pennsylvania, Biden has received 3,345,724 votes to Trump's 3,311,310, a 49.6% to 49.1% advantage.

When asked about the media outlets calling the race for Biden, Giuliani scoffed.

"They don't decide the election," he said. "Don't be ridiculous. Networks don't get to decide elections. Courts do."

The White House statement said the Trump campaign will begin prosecuting its case Monday.

"The American people are entitled to an honest election: that means counting all legal ballots, and not counting any illegal ballots," it said.

Throughout the campaign, Trump has criticized the expansion of mail-in voting, saying mail-in ballots are much more susceptible to fraud.

In Pennsylvania and other states, Giuliani said Republican poll watchers were not allow to observe election officials as they opened and registered mail-in ballots as required by law.