Updated 4:23 p.m. ET

GOP presidential contender Mitt Romney is calling on a defiant Rep. Todd Akin to step aside in the Missouri Senate race.

Akin, a six-term House member, has been under fire since saying Sunday that pregnancy could be prevented in the case of "legitimate rape" because "the female body has ways to try to shut that whole thing down."

BLOG: Akin seeks forgiveness in TV ad

STORY: GOP cuts support from Akin

Akin faces Democratic incumbent Claire McCaskill for a seat that Republicans hope will help them gain majority control in the Senate.

"As I said yesterday, Todd Akin's comments were offensive and wrong and he should very seriously consider what course would be in the best interest of our country," Romney said in a statement. "Today, his fellow Missourians urged him to step aside, and I think he should accept their counsel and exit the Senate race."

Romney was referring to a statement from Missouri Sen. Roy Blunt and former senators John Ashcroft, Kit Bond, John Danforth and Jim Talent that said Akin is not serving the "national interest" by staying in the Senate race.

Senate Minority Leader Mitch McConnell also joined the louder chorus today and formally called on Akin to quit.

Romney's comments come as Akin faces a 5 p.m. CT/6 p.m. ET deadline to withdraw from the ballot with little difficulty. If he doesn't meet the deadline, Missouri law says Akin would need a court order to be removed from the ballot and that he would have to pay for reprinting costs.

In radio interviews this afternoon, Akin vowed he would not drop his candidacy.

"I said one word in one sentence on one day, and everything changed," Akin told former Arkansas governor Mike Huckabee. "I believe the defense of the unborn and a deep respect for life ... are not things to run away from."

Akin repeated his pledge in a separate interview with conservative radio host Dana Loesch. "Let me just make it clear ... that we are not getting out of this race. We are in this race for the long haul and we are going to win it," he said.

The National Republican Senatorial Committee has said it would pull $5 million in advertising if Akin remained in the race. NRSC Communications Director Brian Walsh said the campaign committee will continue to withhold its "support and resources" if Akin presses on with a "misguided campaign."

"The stakes in this election are far bigger than any one individual. By staying in this race, congressman Akin is putting at great risk many of the issues that he and others in the Republican Party are fighting for, including the repeal of ObamaCare," Walsh said.

Asked why he would stay in the race when prominent members of the GOP want him out, Akin explained to Huckabee that he believes he can continue to be a powerful voice for the sanctity of human life.

"I believe there is something that we're missing here, it's something that many Americans in their heart of hearts feel we need to be talking about, and it's not just the 'abortion' issue, it's the question of life," Akin said today. "Because the fact is, in America the respect for human life is deeply engrained in our hearts."

Akin said his campaign has drawn support from small donors, even as outside groups such as Crossroads GPS have pulled their resources. "I noticed a poll came out and (it) still had me a point ahead of Claire McCaskill," he said.

Akin said he has not done "anything that was morally or ethically wrong as sometimes people in politics do," adding the outcry over his original remarks are "a bit of an over-reaction."

"Our campaign in the past was defined by the fact that we stood on principle and we acted with courage," he said. "What we're doing here is standing on a principle about what America is. I believe this is the right thing for me to do. I will be able to add to the message, in some circles, that is being neglected by the Republican Party.

"That is the heart of a winning campaign," he said.

(Contributing: Catalina Camia)