US President Donald Trump have told gun owners that they have a "true friend in the White House" as he addressed a National Rifle Association (NRA) meeting in Atlanta.

"To the NRA, I can proudly say I will never, ever let you down," he said on Friday, pledging also never to "infringe" on the right of people to keep and bear arms.

"Freedom is not a gift from government. Freedom is a gift from God," he told the powerful lobbying group.

Trump, speaking on the 99th day of his presidency, said he was proud to be the first sitting president to address a major NRA forum since Ronald Reagan in 1983.

He thanked the organisation for backing him in May last year, the earliest it has ever endorsed a presidential nominee.

"You came through for me, and I am going to come through for you," Trump said.

According to US media reports, the NRA gave $30.3m to the Trump campaign.

'Assault' over

Since taking office, Trump has raised the issue of gun ownership rights only obliquely at a few of the campaign-style rallies he has held.

But he has taken steps to roll back some restrictions on gun use and sales put into effect during the Obama administration.

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Trump said on Friday that under his administration the "assault" on the Second Amendment of the US Constitution, which secures the right of the people to own guns, has come to an end.

"No longer will the government be trying to undermine your rights and your freedoms as Americans. Instead, we will work with you by your side."

His Democratic predecessor Barack Obama tried to pass minor gun control legislation following the Sandy Hook School massacre that killed 26 people in 2012.

A few blocks away from the NRA convention, protesters gathered to counter the group's message and to honour victims of gun violence.

Gun control organisations said they would also rally on Saturday in opposition to the "extremist" NRA leadership and its "guns everywhere" agenda.

Everytown for Gun Safety said that the gun lobby's agenda contributes to the more than 90 Americans shot and killed and the hundreds more injured every day in the US by gun violence.