A Republican is facing pressure to quit a Senate race over his remarks that women's bodies could prevent pregnancy in cases of "legitimate rape".
Leading condemnation of Representative Todd Akin, President Barack Obama said "rape is rape".
Fellow Republicans have called on Mr Akin to withdraw his candidacy for Missouri's Senate seat.
Republican presidential candidate Mitt Romney swiftly distanced himself from Mr Akin's comments.
The Missouri congressman has since apologised, saying in a TV ad published by Politico that he had used the "wrong words the wrong way".
Missouri Senate candidate Todd Akin has recorded a television ad asking for "forgiveness" from the voters of his state and acknowledging that he used "the wrong words in the wrong way" when he suggested last weekend that rape rarely leads to pregnancy.
When he cancelled a scheduled interview with CNN's Piers Morgan on Monday, the talk show host mocked him by speaking to an empty chair and accusing him of cowardice.
During the interview for KTVI-TV on Sunday, Mr Akin was questioned about his no-exceptions view on abortion, a highly charged issue in the US.
Asked if he would like abortion to be banned even if a pregnancy was the result of rape, the 65-year-old replied: "It seems to me, from what I understand from doctors, that is really rare.
"If it's a legitimate rape, the female body has ways to try to shut that whole thing down.
"But let's assume that maybe that didn't work or something: I think there should be some punishment, but the punishment ought to be of the rapist, and not attacking the child."
At the White House on Monday, Mr Obama said the comments underscored why politicians - most of whom are men - should not make health decisions on behalf of women.
"The views expressed were offensive," he told reporters.
"Rape is rape and the idea that we should be parsing and qualifying and slicing what types of rape we are talking about doesn't make sense to the American people and certainly doesn't make sense to me."
The campaign of Mr Romney, who will challenge President Obama for the White House in November, quickly rebuked Mr Akin.
A spokesman for Mr Romney said that both the candidate and his running mate, Paul Ryan, disagreed with the Missouri congressman.
He also stressed that "a Romney-Ryan administration would not oppose abortion in instances of rape".
The Republican Party told Mr Akin it would now not be spending any money on behalf of his campaign.
National Republican Senatorial Committee Chairman John Cornyn said Mr Akin's comments were "indefensible" and the candidate needed to "carefully consider" what was best for him, his family and the Republican Party.
The AP reported that the NRSC was pulling $5m in funding from the race.
In an interview with CNN, Republican national committee chair Reince Priebus called Mr Akin's comments "biologically stupid" and "bizarre".
But in a radio interview with former Republican White House hopeful Mike Huckabee earlier on Monday, Mr Akin said he would not pull out of the race.
Democratic Missouri incumbent, Senator Claire McCaskill, who has been trailing in opinion polls ahead of November's election, said challenger's remarks were "beyond comprehension".
In 2011, Mr Akin co-sponsored a bill that would have limited the government help available to women seeking abortions in the case of rape to cases of "forcible rape". After a public outcry, the House Republican party changed this language.