Former US President Donald Trump has rejected calls for tighter gun controls after the Texas school shooting.

Instead, on Friday he called for firearms to defend himself against "evil."

"The existence of evil in our world is no reason to disarm law-abiding citizens," Trump said at the annual meeting of the US arms lobby organization NRA.

"The existence of evil is one of the best reasons to arm law-abiding citizens."

An 18-year-old killed 21 people, including 19 schoolchildren, with an assault rifle in an elementary school in the small Texas town of Uvalde on Tuesday.

He was eventually shot dead by police officers - but only about an hour after he entered the school, which has led to growing criticism of the emergency services.

Trump is calling for a major overhaul of school security

“The various gun control measures being pushed by the left would have done nothing to prevent the horror that took place.

Nothing at all,” Trump said at the conference, which was accompanied by protests.

The ex-president read out the names of all 19 children he described as victims of a runaway "maniac".

He called the gun control efforts "grotesque".

"Cynical politicians" would try to take advantage of crying families to increase their own power and curtail constitutional rights.

They would advance their "extreme political agenda."

"We must all come together, Republicans and Democrats - in every state and at every level of government - to finally strengthen our schools and protect our children," Trump said.

What is needed is “a general overhaul of the safety precautions in schools in this country”.

The worst US school shooting in a decade has sparked outrage across national borders and sparked a new debate about lax gun laws in the US.

The NRA held on to its three-day annual meeting despite the carnage.

However, several speakers, including Texas Gov. Greg Abbott, canceled their participation in the event after the massacre.

The organization, which is as influential as it is controversial, has been successfully fighting tightening gun laws for decades.

In the wake of the elementary school shooting, the Republican Party in Washington proposed protecting schools with increased security — including armed guards at a single entrance and exit — rather than restricting gun ownership.