Image copyright AP Image caption Gun violence is Obama's biggest frustration, he says

US President Barack Obama is to widen background checks on buyers of firearms, in a series of measures to address gun violence.

The plans will be announced on Tuesday by the president, despite opposition from Congress to new gun laws.

All sellers who operate online or at gun shows will be forced to conduct background checks on potential buyers.

Republican presidential candidate Rand Paul said he would fight the executive actions "tooth and nail".

And several of his Republican rivals said they would erase the measures "on day one" if they win the White House.

More on US gun debate

Why Obama is powerless - the roadblock at Congress

Are you mad or criminal? - the question a gun seller asks

Texas women and their firearms - a photographer taught to shoot at an early age

Do tighter gun laws work? - a state where guns are a way of life

Guns at home - the question parents hate to ask before a playdate

But Mr Obama says his new measures will be within his legal authority and consistent with the Second Amendment, which grants Americans the right to bear arms.

And while they will not solve every violent crime in the US, he said, they will potentially "save lives and spare families the pain" of loss.

Under the plan announced on Monday evening by the White House:

All sellers must be licensed and conduct background checks, overturning current exemptions to some online and gun show sellers

States must provide information on people disqualified due to mental illness or domestic violence

FBI will increase workforce processing background checks by 50%, hiring more than 230 new examiners

Congress will be asked to invest $500m (£339m) to improve access to mental healthcare

The departments of defence, justice and homeland security will explore "smart gun technology" to improve gun safety

Earlier on Monday, the president heard recommendations from Attorney General Loretta Lynch, FBI Director James Comey and other top law enforcement officials.

He told the BBC last year his failure to pass effective gun laws was his biggest regret.

Media playback is unsupported on your device Media caption US's ex-top lawyer supports Obama's law but not his methods

The Republican speaker of the House of Representatives, Paul Ryan, accused President Obama of "dismissiveness" towards Americans who value the right to bear arms.

"This is a dangerous level of executive overreach, and the country will not stand for it," he said in a statement.

At a gun show - North America editor Jon Sopel

One charming man I spoke to had a stall of fine old pieces, including a Remington rifle from the 1970s. Because he wasn't registered, all I had to do was show him a driver's licence - and answer this question: am I a felon or mad?

Say no to that, and all I had to do was hand over the cash and the gun was mine with as much ammunition as I could carry. And as he pointed out to me, if I lied, how would he know?

There were also individuals walking around the show carrying rifles and revolvers, with flags coming out of the muzzle saying "for sale" - again no restrictions at all for people who just wanted to flog their old firearm.

These are some of the issues that the president wants to address with his executive action.

Read Jon's piece in full