U.S. President Barack Obama delivers a statement at the Treasury Department in Washington on June 14, 2016. Reuters/Carlos Barria

The White House accused U.S. senators of a "shameful display of cowardice" on Tuesday and said they failed the American people by not advancing any gun control measures after the nation's largest mass shooting in Orlando, Florida, last week.

"Gun violence requires more than moments of silence," President Barack Obama said on Twitter. "It requires action. In failing that test, the Senate failed the American people."

Earlier, White House spokesman Josh Earnest appeared on morning television news shows excoriating the U.S. Senate for rejecting on Monday four gun bills aimed at keeping firearms away from people with suspected ties to militants.

"What we saw last night on the floor of the United States Senate was a shameful display of cowardice," Earnest said on MSNBC.

After Monday's votes, the Senate turned away from gun control, at least temporarily, to debate a different tactic for battling domestic attacks that could be inspired by the Islamic State group, also known as ISIS, and other foreign militant groups.

Senators were aiming to vote by Wednesday on legislation by Sen. John McCain of Arizona expanding the FBI's ability to conduct secret surveillance in counterterrorism investigations.

"This week we’ll have the opportunity to strengthen our ability to combat lone wolf terrorists and connect the dots so we are better able to prevent terrorist attacks in the United States" such as the Orlando massacre, Senate Majority Leader Mitch McConnell said.

The Orlando gunman, Omar Mateen, had pledged allegiance to ISIS during the June 12 rampage in which he killed 49 people and wounded 53 at a gay nightclub before being fatally shot by police.

New Gun Control Measures

Republican Sen. Susan Collins of Maine was trying to keep gun control attempts alive. She was expected on Tuesday to introduce a measure that would curb weapons sales to people on a narrow terrorism watch list.

Democrats' efforts to pass a broader prohibition failed on Monday.

It was not yet clear whether Collins' plan would draw significant bipartisan support or whether McConnell would even schedule a vote on her legislation, which likely would draw opposition from the National Rifle Association, a close ally of many Republican lawmakers.

The NRA has worked hard to defeat gun control measures, including attempts in the wake of mass shootings such as the one in Orlando.

Gun control groups, meanwhile, promised to intensify their push for legislative action, but not just in Washington.

Shannon Watts, founder of Moms Demand Action for Gun Sense in America, said her group, besides supporting pro-gun control candidates for the U.S. Congress, would work to strengthen gun sale background check laws “state by state until Congress acts,” in states including Maine and Nevada.

"If the NRA and their lapdogs in the Senate thought moms would feel dispirited and back down they are sorely mistaken,” Watts told reporters in a teleconference.

Earnest said the bills put forth for votes on Monday evening should have drawn strong bipartisan support aimed at shoring up the country's defenses by keeping firearms away from people on terrorism watch lists.

He said U.S. law enforcement officials are concerned that there are individuals in the United States who could have ties to terrorism or are susceptible to online recruitment efforts of ISIS.

"And right now there is not a law on the books that prevents those individuals from walking into a gun store and buying a gun," Earnest said.

The Senate votes against the measures restricting gun sales were a bitter setback to advocates who have failed to get even modest gun curbs through Congress despite repeated mass shootings.

The gun control measures lost in largely party line votes that showed the political power in Congress of gun rights defenders and the NRA.

"Republicans have run around and spent the last week saying ‘radical Islamic extremism’ to anybody who will listen,” Earnest said. "But when it actually comes to preventing those extremists from being able to walk into a gun store and buy a gun, they're AWOL. They won't do anything about it because they're scared of the NRA. That's shameful."