LACROSSE, Wisconsin (AFP) - Republican presidential candidate John McCain's campaign on Friday unveiled a new ad charging that Democrat Barack Obama associated with a "terrorist," and then "lied" about it. The negative spot, called "Ambition" and airing across the United States, takes aim at Obama's ties to Bill Ayers, a 1960s activist McCain's campaign calls a "terrorist." McCain is hoping to cast doubts on the Illinois senator's links to Ayers, now 63, who founded a violent group called the Weather Underground more than four decades ago before becoming a professor. "The ad highlights Barack Obama's blind ambition that led him to work with unrepentant domestic terrorist Bill Ayers, but when running for president, lie about his longstanding relationship and his bad judgment," the McCain campaign said. "Like Barack Obama, his Congressional liberal allies demonstrated their bad judgment in fighting for risky sub-prime loans and against more regulation. Today, millions of Americans are paying for the bad judgment Barack Obama and Congressional liberals demonstrated concerning housing policy," the campaign added. The Weather Underground movement, classified by the FBI as a "domestic terrorist organisation," carried out a series of attacks in protest against the Vietnam War, including on the Pentagon and the US Capitol. The group mainly targeted buildings, but in sporadic attacks, and a bungled 1981 robbery not involving Ayers, the group was responsible for the deaths of several policemen. Ayers escaped prison when charges were dropped in 1974 due to FBI misconduct. He told the New York Times in an article published on Sept 11, 2001 that he felt no regret about his actions.  Ayers is now a professor of education at the University of Illinois-Chicago, a prolific author on educational matters and former advisor to the Chicago mayor Richard Daley. Reports of Ayers' links to Obama surfaced earlier in the year but were given new impetus by an investigation by The New York Times carried on the paper's front page. The 2,000-word article detailed instances where Obama had come into contact with Ayers, either through their anti-poverty and education community work in Chicago or sporadic social contacts. The two first met in 1995, when Ayers worked to bring to Chicago the Annenberg Challenge, a 50-million-dollar school grant, and then-community organiser Obama was recruited for the effort. They met again shortly after when Ayers hosted a campaign event in his home and then-Illinois state senator Alice Palmer chose Obama as her successor. Ayers and Obama subsequently served as board members on a charitable foundation, The Woods Fund, from 1999 to 2001. Obama campaign spokesman Ben LaBolt recently told CNN television that the pair have not spoken by phone or exchanged e-mail messages since Obama became US senator in 2005. The two live in the same Hyde Park neighbourhood of Chicago and, LaBolt said, they last met in a chance encounter on the street over a year ago. The New York Times report has been seized on by Obama's opponents for saying that the senator has "played down his contacts with Ayers" but the article concluded that "the two men do not appear to be close." Obama has called Ayers "somebody who engaged in detestable acts 40 years ago when I was eight years old."