Presidential candidate Donald Trump briefly called for "some form of punishment" for women who have abortions, if abortion became illegal.
His initial comments made during a town hall event with cable network MSNBC sparked a wave of criticism.
However, Mr Trump quickly reversed his position, saying only the person who performed the abortion should be punished.
But he maintained: "My position has not changed."
The front-runner supports a ban on abortions, with certain exceptions.
Abortion has been legal in the United States since 1973 after a landmark Supreme Court ruling.
Only the Supreme Court or a constitutional amendment has the power to overturn Roe v Wade and make abortion illegal.
Once a Democrat, Mr Trump has been criticised for supporting abortion rights in the past.
The Republican party's official position is that abortion should be illegal. Conservative politicians and anti-abortion activists who view abortion as akin to murder, however, tend to avoid outlining any criminal punishment for women who undergo the procedure, instead targeting the doctors responsible.
The reason for this is simple - to make abortion bans more acceptable to a general public that does not want to see possibly distraught women grappling with unwanted pregnancies sent to prison.
Donald Trump, as he is wont to do, just trampled through this carefully constructed conservative political dance with all the grace of a rhinoceros at a tea party. Thanks to his assertion, after prodding, that women should face "some form of punishment" for having an illegal abortion, the conservative pro-life movement is going to be forced to defend their beliefs on uncomfortable ground. Republican candidates will be asked, again and again, to defend or denounce Mr Trump's comments.
This is exactly the kind of scenario that terrifies Republican politicians about Mr Trump as their party's nominee. His ill-considered remarks and shoot-from-the-hip approach to media interviews could be a political minefield for their candidates in the autumn.
In all likelihood it's just a taste of things to come.
However, some anti-abortion groups criticised Mr Trump's initial comments as extreme.
"Mr Trump's comment today is completely out of touch with the pro-life movement and even more with women who have chosen such a sad thing as abortion," said Jeanne Mancini, President of the March for Life Education and Defense Fund.
"No pro-lifer would ever want to punish a woman who has chosen abortion."
Democratic front-runner Hillary Clinton has been an outspoken critic of Mr Trump's stance on women's issues.
"Just when you thought it couldn't get worse. Horrific and telling," said Mrs Clinton after his latest comments.
Texas Senator Ted Cruz, Mr Trump's closest rival in the Republican race, also condemned the billionaire.
"Once again Donald Trump has demonstrated that he hasn't seriously thought through the issues, and he'll say anything just to get attention," Mr Cruz said.
His spokesman Brian Phillips added on Twitter: "Don't overthink it: Trump doesn't understand the pro-life position because he's not pro-life."
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Republican leaders have expressed concern about Mr Trump's prospects in the general election because polls show that the New York businessman is extremely unpopular with female voters.
Mr Trump has come under fire for disparaging women including former presidential candidate Carly Fiorina and TV presenter Megyn Kelly.
"If Trump's words about women - calling us 'disgusting', 'slobs' and 'fat pigs' - didn't scare us, this should," said Kate Black of Emily's List, a group committed to electing female Democrats who support abortion rights.
His campaign manager, Corey Lewandowski, was arrested on Tuesday, accused of a minor assault on a female reporter. Mr Trump has vehemently defended Mr Lewandowski.
Anti-abortion activists traditionally have avoided placing blame on women who undergo abortions, but have focused on those who perform the procedure.
In recent years, conservatives have sought to tighten restrictions on abortion clinics and doctors rather than seek an outright ban.
Abortion rights advocates say these measures are meant to restrict women's access to abortion.
The new laws are particularly widespread in conservative southern states.