FAIRFAX, Va. — President Barack Obama tore into the National Rifle Association on Thursday as he sought support for his actions on gun control, accusing the powerful lobby group of peddling an “imaginary fiction” that he said has distorted the national debate about gun violence.

In a prime-time, televised town hall meeting, Obama dismissed what he called a “conspiracy” alleging that the federal government — and Obama in particular — wants to seize all firearms as a precursor to imposing martial law. He blamed that notion on the NRA and like-minded groups that convince its members that “somebody’s going to come grab your guns.”

“Yes, that is a conspiracy,” Obama said. “I’m only going to be here for another year. When would I have started on this enterprise?”

Obama defended his support for the constitutional right to gun ownership while arguing it was consistent with his efforts to curb mass shootings. He said the NRA refused to acknowledge the government’s responsibility to make legal products safer, citing seatbelts and child-proof medicine bottles as examples.

Taking the stage at George Mason University, Obama accused the NRA of refusing to participate in the town hall despite having its headquarters nearby.

“Since this is a main reason they exist, you’d think that they’d be prepared to have a debate with the president,” Obama said.

NRA spokesman Andrew Arulanandam said beforehand that the group saw “no reason to participate in a public relations spectacle orchestrated by the White House.” Several NRA members were in the audience for the event, which was organized and hosted by CNN. And the NRA pushed back on Twitter in real time, noting at one point “none of the president’s orders would have stopped any of the recent mass shootings.”

The White House has sought to portray the NRA, the nation’s largest gun group, as possessing a disproportionate influence over lawmakers that has prevented new gun laws despite polls that show broad U.S. support for measures like universal background checks. Last year, following a series of mass shootings, Obama pledged to “politicize” the issue in an attempt to level the playing field for gun control supporters.