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Donald Trump set himself on a collision course with the National Rifle Association as America's biggest gun lobby suggested he wanted to "punish" innocent gun owners and strip them of their Constitutional rights.

The US president, who was enthusiastically endorsed by the NRA in the 2016 election, called for substantial changes to gun laws in the wake of last month's school shooting in Florida which cost 17 lives.

It came as Walmart, the world's largest retailer and America's biggest gun seller, announced it was raising the minimum age for buying weapons and ammunition from 18 to 21.

Perhaps the most unexpected suggestion from Mr Trump was that police should be able to confiscate people's firearms without a court order to prevent potential tragedies.

At an hour-long televised meeting with Democrat and Republican senators he said: "I like taking the guns early. Take the guns first, go through due process second."