US President Donald Trump used a Christian rally in honour of armed forces veterans on Saturday to warn about dangers to religious freedom and lash out at the 'fake media' he believes are trying to undermine his agenda.

The Celebrate Freedom event at the John F Kennedy Center for the Perfoming Arts in Washington was hosted by Trump backer Pastor Robert Jeffress and his church, First Baptist in Dallas, Texas, with Salem Media Group.

Jeffress introduced Trump as a personal friend who 'has exceeded our expectations, in reviving the economy, rebuilding our military, respecting our veterans, and restoring the greatest freedom of all — the free exercise of our faith', according to Dallas News. 

'Millions of Americans believe that [Trump's victory] represented God giving us our next chance, perhaps our last chance, to make America great again,' Jeffress said.

Trump said terrorism was 'one of the most grave and dire threats to religious freedom in the world today'.

In an apparent reference to his attempts to implement a 'Muslim ban' on travel to the US, partially uphelp by judges last week, he said: 'We cannot allow this terrorism and extremism to spread in our country, or to find sanctuary on our shores or in our cities.

'We want to make sure that anyone who seeks to join our country shares our values and has the capacity to love our people.'

He appeared to repeat a claim – denied by most historians – that the US was founded as a 'Christian nation', saying: 'Since the signing of the Declaration of Independence 241 years ago, America always affirmed that Liberty comes from our Creator.

' Our rights are given to us by God, and no earthly force can ever take those rights away.'

He used the event to repeat his attacks on the Washington establishment, saying: 'For too long, politicians have tried, oh have they tried, to centralise the authority among the hands of a small few.

'Bureaucrats think they can run over your lives, overrule your values, meddle in your faith, and tell you how to live, what to say, and where to pray.'

He added: 'And above all else we know this: In America, we don't worship government, we worship God.'

Saturday also saw Trump renew his Twitter assault on Morning Joe co-hosts Mika Brzezinksi and Joe Scarborough, saying: 'Crazy Joe Scarborough and dumb as a rock Mika are not bad people, but their low rated show is dominated by their NBC bosses. Too bad!'