Alan Diaz, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney speaks during a campaign stop at the Palm Beach Convention Center in West Palm Beach, Fla., Thursday, Jan. 12, 2012.

GREER, S.C. — Former Massachusetts Gov. Mitt Romney on Thursday insisted he is "pro-life" and said he's raising the issue on the campaign trail to counter his rivals' attacks.

"I understand that there are some attack ads coming my way that question" his commitment to life, Romney told reporters gathered at a motorcycle dealership in Greer, S.C. "Obviously it's important for me to remind people that I'm pro-life."

Former House Speaker Newt Gingrich's campaign is running ads in South Carolina attacking Romney for changing his position on abortion. It's part of an onslaught of negative ads Romney is facing in the first-in-the-South primary, some from his rivals and some from their wealthy SuperPAC allies.

Romney arrived in South Carolina Wednesday and held a rally in Columbia, where he added extra emphasis to his typical campaign speech focused on protecting life.

"I'm convinced that the principles of opportunity, and freedom and the protection of life were not temporary but are permanent," Romney said Wednesday. And on Thursday, campaigning in the conservative Upstate, he repeated "life, life" twice as he recited the Declaration of Independence.

Gingrich has been hammering away at Romney's claim to conservative credentials, calling Romney a "Massachusetts moderate." Gingrich said Thursday he intends to emphasize Romney's views on social issues such as abortion, gun control and gay marriage in the days leading up to South Carolina's Jan. 21 primary.

Romney also is defending his record as a venture capitalist, repeating his contention that the company he ran was set up to save businesses where possible, although he's admitted that in private business, these efforts aren't always fruitful.

Romney came to South Carolina Wednesday as the unmistakable front-runner in the GOP presidential sweepstakes. But many of the state's voters are conservative Christians and tea party supporters, and Romney struggled here four years ago. He came in fourth.

Romney said Thursday the environment has changed enough that he could win here.

"Four years ago, we were really focused on Iraq and what was happening there and the surge. And that was an area that really was in John McCain's wheelhouse," Romney said. "Now the economy is the issue people are most concerned about. That's in my wheelhouse."

"This is a time when people care about the economy and the scale of government. It's the message of the tea party, it's the message of the Republican Party," he said.

Romney was leaving South Carolina Thursday to hold a midday rally in West Palm Beach, Fla., where absentee voters are already mailing in ballots. The primary is Jan. 31.

But first he stopped to admire the motorcycles on display at Cherokee Trikes and More after he wrapped up the rally in the back warehouse. He stood with an array of motorcycles behind him as he took reporters' questions — but refused to sit on a motorcycle and pose for pictures.

Instead, he joked: "And, what, put a helmet on, Dukakis style?"