Donald Trump has vowed to end the "eight year assault" on Americans' rights to bear arms, in the first speech delivered by a president to the National Rifle Association in more than three decades.

Mr Trump became the first president to address members of the country's most powerful gun lobby since Ronald Reagan in 1983, hoping to renew his standing among a conservative base wary after watching the President reverse course on a series of campaign promises.

"The eight-year assault on your Second-amendment freedoms has come to a crashing end," Mr Trump said, referring to the presidency of Barack Obama, his predecessor.

"I will never ever infringe on the right of the people to keep and bear arms."

"You have a true friend and champion in the White House," he said. "No longer will federal agencies come after law abiding gun owners.

"No longer will the government be trying to undermine your rights and freedoms as Americans. We want to assure you of the sacred right of defence for all our citizens."

For Mr Trump, the speech was a chance to return to the campaign-style rallies that he seemed to so enjoy during the election.

Marking his first 100-days in office on Saturday, Mr Trump is under pressure to demonstrate his commitment to the principles he laid out as a Republican candidate.