Republican White House hopeful John McCain fired back at critics to "lighten up and get a life" for his joke about bombing Iran.

The liberal group MoveOn.org announced plans on Friday to launch an ad campaign against McCain because America "can't afford another reckless president."

McCain's campaign responded quickly to MoveOn.org's criticism.

“It comes as no surprise that America’s most liberal interest group would attack John McCain’s belief that we cannot allow Iran to destroy Israel,” said spokesman Matt David. “After all, MoveOn.org posted ads comparing President Bush to Hitler during the last presidential election.”

Speaking to a group of veterans in the Murrells Inlet VFW Hall in South Carolina, McCain, perhaps affected by cold medicine, had been speaking for nearly 90 minutes when he invoked the Beach Boys' melody Barbara Ann to respond to a question about when the U.S. would "send an air mail message to Iran."

McCain answered by going into the song's paraphrased chorus: “Bomb bomb bomb, bomb bomb Iran.”

Click here to watch McCain sing.

It's not the first time the song has been borrowed to express the sentiment. After the 1979 American embassy hostage crisis, a parody was created that has been revised in varying forms since the beginning of the war in Iraq.

McCain answered a reporter's question about it at a press conference in Las Vegas on Thursday.

"Please, I was talking to some of my old veteran friends," McCain said. "My response is, 'lighten up and get a life.'"

The group plans to spend about $100,000 to air a commercial on network and some cable television stations in Iowa and New Hampshire, states that hold early contests in the presidential nomination process, spokesman Alex Howe said Friday.

The group ran ads in the same states in January, criticizing the Arizona senator's support for sending more troops to Iraq.

McCain's comments, posted on YouTube.com, had been viewed at least 118,056 times as of Friday morning.

The Associated Press contributed to this report.