New York mayor Michael Bloomberg is bankrolling a $12m advertising blitz in a bid to pressure Congress into adopted stricter gun controls.

The television ads are set to run in 13 key states during the congressional recess and are aimed at influencing an upcoming Senate vote on gun reforms.

Announcing the move, Bloomberg – the co-chair of Mayors Against Illegal Guns and one of the US's most high-profile advocates of tighter controls – said: "These ads bring the voices of Americans – who overwhelmingly support comprehensive and enforceable background checks – into the discussion to move senators to immediately take action to prevent gun violence."

But pro-gun lobby group the National Rifle Association (NRA), accused the New York mayor of attempting to "intimidate senators".

The new ads feature a man holding a gun on the back of a pickup truck. In one, he says he will defend the second amendment but adds that "with rights come responsibilities". He goes on to urges viewers to tell Congress to support background checks.

In the other ad posted on the Mayors Against Illegal Guns website, the man says "background checks have nothing to do with taking guns away from anyone", rather they are aimed at preventing criminals and mentally ill people from owning deadly weapons.

The advertising plan comes days after the Senate disappointed advocates of greater controls by effectively abandoning a proposal to ban military-style assault weapons.

Last Tuesday, Senate leader Harry Reid said than the ban would not form part of a bill members are due to vote on, as it did not have the support needed to force it through Congress.

But in his weekly radio address on Saturday, President Barack Obama called on Washington to vote on the assault rifle ban in any case.

Describing the proposal and others including background checks as common-sense measures, he added: "They are supported by a majority of the American people. And I urge the Senate and the House to give each of them a vote."

Likewise Bloomberg called on the Senate to put gun control measures to the vote. "We demanded a plan and we got one. We demanded a vote and we'll get one. Now we're doing what we can to pass a bill that will save lives," he said.

The renewed focus on addressing America's problem with gun violence followed a series of mass shootings in 2012, culminating in the deaths of 20 children and six adults at a Connecticut elementary school.

But initial optimism that meaningful reform would take place has become bogged down in the realities of Washington politics.

Meanwhile public opinion appears to be wavering. In the immediate aftermath of the Connecticut school massacre, some 52% of Americans were found to be in favour of major restrictions on guns. According to a CNN/ORC poll released last week, that number had dropped to 43%.

Asked on NBC's Meet the Press if he thought momentum on the issue had gone, Bloomberg said: "It would be a great tragedy for this country and for tens of thousands of lives if it is lost."

He added that he was "cautiously optimistic" that reform would be passed. But standing in the path of any restrictions is the NRA, who are likely to mount a fierce counter-campaign to Bloomberg's ads.

Responding to Bloomberg's announcement, Wayne LaPierre, NRA chief executive, told Meet the Press "He can't buy America", adding: "He can't spend enough of his $27bn to impose his will on the American public." © Guardian News and Media 2013