WASHINGTON/WILMINGTON, Del., Nov 7 (Reuters) - Democrat Joe Biden won the presidency on Saturday after a bitter election campaign and promised he would work to unify a deeply divided country, even as President Donald Trump refused to accept defeat.

Biden's victory in the battleground state of Pennsylvania put him over the threshold of 270 Electoral College votes he needed to clinch the presidency, ending four days of nail-biting suspense and sending his supporters into the streets of major cities in celebration.

"The people of this nation have spoken. They have delivered us a clear victory, a convincing victory," Biden told cheering supporters in a parking lot during his victory speech in his home town of Wilmington, Delaware.

"I pledge to be a president who seeks not to divide, but to unify," he said, then addressed Trump's supporters directly.

"Now, let's give each other a chance. It's time to put away the harsh rhetoric, lower the temperature, see each other again, listen to each other again," he said. "This is the time to heal in America."

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Democratic vice-presidential nominee Kamala Harris and Democratic 2020 U.S. presidential nominee Joe Biden greet supporters at an election rally, after news media announced that Biden has won the 2020 U.S. presidential election, in Wilmington, Delaware, U.S., November 7, 2020. Andrew Harnik/Pool via REUTERS
Democratic vice-presidential nominee Kamala Harris and Democratic 2020 U.S. presidential nominee Joe Biden greet supporters at an election rally, after news media announced that Biden has won the 2020 U.S. presidential election, in Wilmington, Delaware, U.S., November 7, 2020. Andrew Harnik/Pool via REUTERS

He was introduced by his running mate, U.S. Senator Kamala Harris, who will be the first woman, the first Black American and the first American of Asian descent to serve as vice president, the country's No. 2 office.

Congratulations poured in from abroad, including from conservative British Prime Minister Boris Johnson, Canadian Prime Minister Justin Trudeau and German Chancellor Angela Merkel, making it hard for Trump to push his repeated claims, without evidence, that the election was rigged against him.

Trump, who was golfing when the major television networks projected his rival had won, immediately accused Biden of "rushing to falsely pose as the winner."

"This election is far from over," he said in a statement.

Trump has filed a raft of lawsuits to challenge the results but elections officials in states across the country say there has been no evidence of significant fraud, and legal experts say Trump's efforts are unlikely to succeed.

(Reporting by Trevor Hunicutt, Steve Holland and Jeff Mason; Additional reporting by Michael Martina in Detroit, Michigan; Mimi Dwyer in Phoenix, Arizona; Jarrett Renshaw in Philadelphia, Jan Wolfe in Boston and Doina Chiacu, Alexandra Alper, Raphael Satter, Makini Brice, Aram Roston, Susan Cornwell and Richard Cowan in Washington; Writing by Sonya Hepinstall and John Whitesides; Editing by Ross Colvin and Daniel Wallis)