A top Washington-based evangelical leader has endorsed Donald Trump and encouraged his large following to do the same.

Family Research Council (FRC) leader Tony Perkins, who has up to now held back from declaring his support in the presidential race, last night took to the stage at the Quickens Loan Arena to support the candidate.

"Donald Trump is the nominee of the Republican Party, and I will be voting for Donald Trump in November, and I will urge my fellow Americans to do the same," Perkins said.

"Donald Trump has committed to upholding and protecting the first freedom and therefore our ability as citizens to unite our nation once again under God," he continued. "Let us go forth from here and do that work."

The Washington blog The Hill said that the endorsement by Perkins, who has 25,000 Twitter followers, "could be a tipping point for the religious right moving behind the party's newly-minted nominee."

Nearly eight in 10 white evangelical voters say they would vote for Trump if the election were held today, including a third who "strongly" back his campaign, according to a recent Pew survey.

White evangelical Protestants make up one-fifth of all registered voters in the US.

After doubts about whether Trump could attract the conservative Christian vote, because of his colourful private life and divisive language, his campaign has been leant credibility by the appointment of Mike Pence as his running mate.

Pence, a senior Republican and now Vice Presidential candidate, is a former Catholic who has now embraced the evangelical movement.

The FRC is a lobbying organisation founded in 1981 by James Dobson, and campaigns for traditional family values.

Dobson has also backed Trump, having previously supported presidential hopeful Ted Cruz. Dobson said in a statement last night: "I have decided to endorse Donald J Trump for President of the United States, not only because of my great concern about Hillary Clinton. I am supporting Mr Trump primarily because I believe he is the most capable candidate to lead the United States of America in this complicated hour."