President Donald Trump has announced he will "get rid of and totally destroy" a 60-year-old rule that blocks tax-exempt religious groups from endorsing or opposing political candidates.

The so-called Johnson amendment was introduced by then-Senator Lyndon B Johnson in 1954. It threatens churches and other religious institutions with the loss of their tax-exempt status should they overstep the mark.

At the National Prayer Breakfast in Washington DC on Thursday Mr Trump said: "Jefferson asked, 'Can the liberties of a nation be secure when we have removed a conviction that these liberties are the gift of God?' Among those freedoms is the right to worship according to our own beliefs. That is why I will get rid of and totally destroy the Johnson amendment and allow our representatives of faith to speak freely and without fear of retribution—I will do that."

Mr Trump also spoke about a global threat to free worship. He said: "Freedom of religion is a sacred right, but it's also a right under threat all around us and the world is under serious, serious threat in so many different ways.

"I've never seen it so much and so openly. We're going to straighten it out. That's what I do, I fix things. It's time we're going to be a little bit tough."

In an apparent reference to Isis, he added: "We've seen unimaginable violence carried out in the name of religion. Acts of wanton slaughter against religious minorities. Terrorism is a fundamental threat to religious freedom."

The declaration came as an apparent leaked draft of a new executive order set out how specific religious beliefs—reflecting conservative Christian social tenets—could become enshrined as executive policy.

They include "﻿the belief that marriage is or should be recognised as the union of one man and one woman, sexual relations are properly reserved for such a marriage, male and female and their equivalents refer to an individual’s immutable biological sex as objectively determined by anatomy, physiology, or genetics at or before birth, and that human life begins at conception and merits protection at all stages of life".

The draft order seeks to protect the tax-exempt status of organisations that propound those beliefs, as well as to block "adverse action" against groups that discriminate, on religious grounds, in the provision of adoption and fostering services. White House spokesman Sean Spicer did not comment on the specifics of the leak.

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His address to the National Prayer Breakfast, an annual event organised by The Fellowship Foundation, a Christian group, and attended by the President of the day, was not the first time Mr Trump had set out his plan for the Johnson amendment.

Last September he tried to woo evangelical voters with a promise that the US' "Christian heritage will be cherished, protected, defended like you have never seen before". His repeal of the amendment would "give our churches their voice back", he said.

The repeal was one of his 282 campaign promises.