Democrat Joe Biden has been certified as the winner of the presidential election in Pennsylvania, the US state's governor said.

Governor Tom Wolf, a Democrat, tweeted that the Pennsylvania State Department "certified the results of the November 3 election in Pennsylvania for president and vice president of the United States.

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"As required by federal law, I've signed the Certificate of Ascertainment for the slate of electors for Joe Biden and Kamala Harris."

President Donald Trump, who lost the state's 20 electoral votes to Mr Biden, has made Pennsylvania a centrepiece of his unsuccessful legal attempts to invalidate the election results.

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Mr Trump had won the state in 2016 against expectations against Democrat nominee Hillary Clinton.

Earlier this week, a judge in Pennsylvania dismissed a lawsuit from the Trump campaign that aimed to invalidate millions of mail-in votes in the state.

State judge Matthew Brann said the suit was "without merit", with Joe Biden having a lead of more than 80,000 in the state.