President Donald Trump has again pushed his call to arm teachers following last week’s school massacre in Florida, saying it “would solve the problem instantly.”

In a lengthy series of Twitter posts on Thursday night and Friday morning (AEDT), Mr Trump aligned his policy with the powerful National Rifle Association gun lobby, while clarifying that only teachers with military training would be armed.

The February 14 massacre at Marjory Stoneman Douglas High School, in which 17 students and staff members were killed, was the second-deadliest shooting at a US public school and has spurred unprecedented youth-led protests.

Mr Trump initially raised the idea of arming teachers during an emotional, hour-long discussion with people affected by school shootings on Thursday at the White House.

The gathering included students who had survived the Florida attack.

Mark Barden, whose son was killed in the 2012 Sandy Hook Elementary School shooting in Connecticut, said his wife, Jackie, a teacher, would say “school teachers have more than enough responsibilities right now than to have to have the awesome responsibility of lethal force to take a life”.

Mr Trump’s follow up tweets showed him seeking a balance between satisfying those calling for controls on weapons, and not alienating the powerful NRA gun lobby.

But the President later reiterated his strategy, saying specially trained teachers with concealed weapons would be the best deterrent against a “savage sicko” with “bad intentions”.

I never said “give teachers guns” like was stated on Fake News @CNN & @NBC. What I said was to look at the possibility of giving “concealed guns to gun adept teachers with military or special training experience – only the best. 20% of teachers, a lot, would now be able to

— Donald J. Trump (@realDonaldTrump) February 22, 2018

….immediately fire back if a savage sicko came to a school with bad intentions. Highly trained teachers would also serve as a deterrent to the cowards that do this. Far more assets at much less cost than guards. A “gun free” school is a magnet for bad people. ATTACKS WOULD END!

— Donald J. Trump (@realDonaldTrump) February 22, 2018

Mr Trump praised the NRA’s leadership and others working at the organisation as “Great People and Great American Patriots. They love our Country and will do the right thing”.

He added: “Highly trained, gun adept, teachers/coaches would solve the problem instantly, before police arrive. GREAT DETERRENT!”

Later, NRA chief executive Wayne LaPierre delivered a defiant defence of using guns to stop gun violence.

Addressing a gathering of young conservatives, he bolstered Mr Trump’s call to arm teachers and offered free training.

“We must immediately harden our schools,” he said.

“Every day, young children are being dropped off at schools that are virtually wide open, soft targets for anyone bent on mass murder.”

He added that it should not be easier to shoot up a school than a bank or a jewellery store and claimed: “The elites don’t care not one whit about America’s school system and school children.

“Their goal is to eliminate the second Amendment and our firearms freedoms so they can eradicate all individual freedoms.”

Mr Trump praised the efforts of Mr LaPierre and his NRA associates.

What many people don’t understand, or don’t want to understand, is that Wayne, Chris and the folks who work so hard at the @NRA are Great People and Great American Patriots. They love our Country and will do the right thing. MAKE AMERICA GREAT AGAIN!

— Donald J. Trump (@realDonaldTrump) February 22, 2018

Republican Senator Marco Rubio, who has long opposed gun control measures, and a teacher who had protected more than 60 people in her classroom in the Florida massacre, questioned the notion of armed teachers during a CNN discussion.

Mr Trump reiterated he would advocate tightening background checks for gun buyers, with an emphasis on mental health, and lifting the age limit to buy some kinds of guns.

He also stressed he would push for an end to the sale on bump stocks, which allow rifles to shoot hundreds of rounds a minute and which were used during another massacre in Las Vegas last year.

– With AAP