The creators of Big Bird have called on the Obama campaign to withdraw a new advertisement that uses the character in an attack on rival Mitt Romney. The ad mocks the Republican candidate for singling out the public broadcaster behind Sesame Street for spending cuts. Mr Romney said in a presidential debate last week that he would slash funding to PBS, despite liking Big Bird. Opinion polls suggest Mr Romney has hit Mr Obama's lead after the Republican's strong debate performance. With election day looming on 6 November, the two White House rivals campaigned on Tuesday in the key election swing state of Ohio. Big yellow menace? Sesame Workshop, the non-profit behind the long-running children's show, said in a statement that it was a nonpartisan organisation. "We do not endorse candidates or participate in political campaigns," the organisation said. "We have approved no campaign ads and, as is our general practice, have requested that the ad be taken down." Obama spokesman Ben LaBolt said the campaign was considering the request. The US government partially funds PBS and National Public Radio, both targets of conservative politicians. Mr Obama has used Mr Romney's comments in their first debate to attack the Republican candidate's spending priorities. The advertisement pokes fun at Mr Romney with clips of him mentioning Big Bird and PBS throughout the campaign. "One man has the guts to say his name," says the ad, flashing to Mr Romney and then the feathered character. "Big. Yellow. A menace to our economy. Mitt Romney knows it's not Wall Street you have to worry about. It's Sesame Street." A Romney spokesman accused the Obama campaign on Tuesday of not focusing on serious issues. "I just find it troubling that the president's message, the president's focus 28 days from election day, is Big Bird," Kevin Madden told reporters. The latest Reuters poll suggests Mr Romney has erased Mr Obama's advantage with voters on a range of issues, including the economy. A Pew Research Center poll indicated Mr Romney was leading the president by four points. And according to a Gallup poll, Mr Romney was at 49% to Mr Obama's 47% among likely voters. However, Mr Obama was leading in the same survey among registered voters.