Calls for Akin's exit from the race grew Monday, with at least two Republican senators Scott Brown of Massachusetts and Ron Johnson of Wisconsin saying Akin should resign the nomination.
A White House spokesman says Akin's comments on rape are "offensive" and "wrong."
White House Press Secretary Jay Carney said Monday that comments by the Missouri congressman are "factually wrong, medically wrong and offensive."
Akin, who has served six terms, pledged to continue the race against Democratic incumbent Sen. Claire McCaskill.
"The good people of Missouri nominated me, and I'm not a quitter," he said. "And my belief is we're going to take this thing forward and by the grace of God, we're going to win this race."
During the primary campaign, Akin ran TV ads in which Huckabee praised him as "a courageous conservative" and "a Bible-based Christian" who "supports traditional marriage" and "defends the unborn."
Asked in an interview Sunday on KTVI-TV if he would support abortions for women who have been raped, Akin said: "It seems to me, first of all, from what I understand from doctors, that's really rare. If it's a legitimate rape, the female body has ways to try to shut that whole thing down."
Later Sunday, Akin released a statement saying that he "misspoke" during the interview, though the statement did not say specifically which points were in error.
"In reviewing my off-the-cuff remarks, it's clear that I misspoke in this interview, and it does not reflect the deep empathy I hold for the thousands of women who are raped and abused every year," Akin's statement said.
Akin also said he believes "deeply in the protection of all life" and does "not believe that harming another innocent victim is the right course of action."
Brown, considered to be one of the most vulnerable Senate Republicans in the November election, said Akin's comments were "outrageous, inappropriate and wrong,"
"There is no place in our public discourse for this type of offensive thinking," said Brown, who is locked in a tight race with Elizabeth Warren.
Brown said Akin should apologize and resign the Senate nomination.
Johnson, a Wisconsin Republican, said in a tweet that Akin "should step aside today for the good of the nation."
Akin's comments also brought a swift rebuke from the campaign of presumptive GOP presidential nominee Mitt Romney and his running mate, Rep. Paul Ryan of Wisconsin.
Romney and Ryan "disagree with Mr. Akin's statement, and a Romney-Ryan administration would not oppose abortion in instances of rape," Romney spokeswoman Amanda Henneberg said.
Romney went further in an interview with National Review Online, calling Akin's comments "insulting, inexcusable and frankly wrong."
"Like millions of other Americans, we found them to be offensive," Romney said.
In an emailed statement Sunday, McCaskill said it was "beyond comprehension that someone can be so ignorant about the emotional and physical trauma brought on by rape."
This month, the 65-year-old congressman won the state's Republican Senate primary by a comfortable margin. During the primary campaign, Akin enhanced his standing with TV ads in which former Arkansas governor and presidential candidate Mike Huckabee praised him as "a courageous conservative" and "a Bible-based Christian" who "supports traditional marriage" and "defends the unborn."
Ushering Akin from the race is complicated by the fact that he has never been a candidate beholden to the party establishment. Since being elected to Congress in 2000, Akin has relied on a grassroots network of supporters. His Senate campaign is being run by his son.
Behind the scenes, Republican officials were looking for intermediaries trusted by Akin to try to coax him from the race.
Missouri election law allows candidates to withdraw 11 weeks before Election Day. That means the deadline to exit the Nov. 6 election would be 5 p.m. Tuesday. Otherwise, candidates would need a court order to withdraw.
If Akin were to leave, state law holds that the Republican state committee has two weeks to name a replacement. The candidate would be required to file within 28 days of Akin's exit.
Akin, a former state lawmaker who was first elected to the House in 2000, also has a long-established base among evangelical Christians and was endorsed in the primary by more than 100 pastors.