U.S. Republican presidential candidate Mitt Romney took a dig at President Barack Obama on Friday over his birth certificate in comments that re-ignited the controversy over the Democrat's eligibility to be president.
"No one's ever asked to see my birth certificate," Romney told a rally of some 7,000 people in his home state of Michigan.
"They know that this is the place that we were born and raised," he said to the laughter of the crowd, speaking alongside his wife, Ann.
Romney's comments were a reference to the widely discredited belief that Obama, whose father was from Kenya, was not born in the United States and thus is not eligible to be president.
Conservative fringes of the Republican Party -- including high-profile Romney backer Donald Trump -- have argued that Obama was not born in Hawaii as he says.
In an effort to end the "birther" controversy, Obama has released multiple copies of his birth certificate that show he was born in the United States. But some conservatives refuse to let the issue die.
Romney's comments came as Republicans geared up for Monday's opening of a four-day nominating convention, and was the latest distraction from his central argument that Americans need a change from Obama's economic leadership.
Romney's camp sought to downplay his birth certificate remarks, which were made at an outdoor rally at a farm near Detroit.
"The governor has always said, and has repeatedly said, he believes the president was born here in the United States," adviser Kevin Madden said. "He was only referencing that Michigan, where he is campaigning today, is the state where he himself was born and raised."
Romney brought up the issue despite having complained recently that the campaign had taken a nasty tone.
"Throughout this campaign, Governor Romney has embraced the most strident voices in his party instead of standing up to them," Obama campaign spokesman Ben LaBolt said.
"Governor Romney's decision to directly enlist himself in the birther movement should give pause to any rational voter across America," he said.
It was the second controversial comment by Romney in less than 24 hours.
Romney said in Minnesota on Thursday that "big business is doing fine in many places," seemingly contradicting his message that companies are struggling under Obama.
The line echoed an Obama comment about the private sector doing well that the Republican has repeatedly criticized on the campaign trail.