Kellyanne Conway criticized Democrats for reacting to the mass shooting in Las Vegas with calls for gun control. Pool/Getty Images

Kellyanne Conway, the top counselor to President Donald Trump, on Thursday said the White House and many Republican lawmakers welcomed "thoughtful conversations" about gun control in the wake of the deadliest mass shooting in modern US history, but she then laid blame with the Obama administration for not regulating a device that allowed the shooter to mow people down with rapid fire.

The Sunday-night shooting at a Las Vegas music festival left 58 people dead and more than 500 injured.

"We always welcome thoughtful conversation about policy and issues," Conway told "Fox & Friends" on Thursday morning, adding that the right to bear arms was "a bedrock within our Constitution" and "must be protected."

Conway noted that several Republican lawmakers on Capitol Hill had said they were unaware of the existence of the device, known as a bump stock, that allowed the Las Vegas gunman’s semiautomatic rifles, in which the trigger must be pulled once for every shot, to behave like fully automatic weapons.

After suggesting Republicans would be open to regulating bump stocks, Conway attacked Democrats for not having already done so, noting that in 2010 the Bureau of Alcohol, Tobacco, Firearms and Explosives decided not to ban the devices, which remain legal.

"This is a device that Obama's ATF decided would not be regulated in 2010, and I think that's an important part of this conversation," she said.

She then accused prominent Democrats, including Hillary Clinton, Sen. Bernie Sanders, and Sen. Elizabeth Warren, of largely ignoring the issue of gun control, speaking out about it only when politically convenient, including after mass shootings.

"They either have tweeted zero to one times this year about guns," she said. "They've tweeted about Russia dozens of times, they've tweeted about this president innumerable times ... they react and we need to have thoughtful conversations in this country."

Conway made the same argument on CNN's "New Day," accusing Democrats of seizing on mass shootings to promote an issue they otherwise pay little attention to.

"I know the high-horse cavalry loves to run in, thumping their chest after the tragedies," Conway told CNN, "but let's step back and have a thoughtful conversation about everything that is at play here."

CNN host Chris Cuomo pushed back on Conway's claim.

"The president says not now, and then it doesn't happen," Cuomo said. "You make the point yourself ... you say, 'They don't talk about it except when these happen.' Yeah, that's right. Because when it happens there's acute need and there's focus, and when you say, 'We don't want to talk about it now,' you're ignoring the urgency and you're hoping it goes away."

Conway also accused Clinton and others of "jumping to Twitter while parents were literally still combing the hospitals, if not the rubble, for their missing loved ones."

Republicans have for decades thwarted attempts to regulate guns, including universal background checks, restrictions on people on terrorism watch lists obtaining firearms, and limits on the size of ammunition magazines.

Sen. Dianne Feinstein, a California Democrat who has long advocated gun control, introduced legislation this week to ban bump stocks — something she attempted to do in 2013 as part of an unsuccessful renewal of the assault-weapons ban. Feinstein argued that the latest measure, which is supported by about two dozen Democrats, was narrow and would not be a significant victory for gun control but was simply common sense.

"I mean, if not this, what?" she said. "It doesn't take a weapon away. It just means you can't convert it into something it's not meant to be."

Feinstein has said her daughter had planned to attend the Route 91 Harvest festival, the target of Sunday night’s shooting, but ended up not going.