Publishedduration10 minutes agoimage copyrightAFP/Getty Imagesimage captionChris Christie (right) is a longtime ally of President Trump

A prominent ally of Donald Trump has urged him to drop his efforts to overturn his loss to Joe Biden in the US presidential election.

Former New Jersey Governor Chris Christie called the president's legal team a "national embarrassment".

President Trump has refused to concede the election, making unsubstantiated claims of widespread electoral fraud.

Many Republicans have supported his legal efforts but a small but growing number have broken ranks.

On Saturday Mr Trump suffered a major blow in Pennsylvania, after a judge dismissed a lawsuit from the Trump campaign seeking to invalidate millions of mail-in votes in the battleground state.

In a scathing ruling, Judge Matthew Brann said his court had been presented with "strained legal arguments without merit and speculative accusations".

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The move paves the way for Pennsylvania to on Monday certify Mr Biden's win – the Democratic president-elect leads there by more than 80,000 votes.

Mr Biden is projected to defeat President Trump 306 to 232 in the US electoral college, which determines who becomes president – far above the 270 he needs to win.