(CNN) -- Mitt Romney led fresh Republican attacks on Friday over Vice President Joe Biden's debate remark about security concerns at the U.S. diplomatic compound in Libya where four Americans - including Ambassador Christopher Stevens -- were killed in a terrorist attack.
The GOP presidential challenger accused Biden of contradicting State Department officials when he said at Thursday's debate against Romney's running mate, Rep. Paul Ryan, that "we weren't told they wanted more security" at the diplomatic facility in Benghazi.
The mission came under attack by armed militants on the 11th anniversary of the September 2001 al Qaeda attacks on New York and Washington.
However, State Department officials told a congressional hearing on Wednesday that they requested more security but were turned down by headquarters in Washington.
"When the vice president directly contradicts the sworn testimony of state department officials ... the American people deserve to know what happened," Romney told a campaign event in the battleground state of Virginia.
Biden made no mention of Libya in his lone campaign appearance on Friday in Wisconsin, instead focusing on his main campaign themes that Romney and Republicans favor protecting the wealthy over helping the middle class.
The vice president's comment in the feisty debate with Ryan provided an opening for Romney's campaign to continue its criticism of the Obama administration's foreign policy, a topic on which polls show voters favor the president over his Republican opponent ahead of the November 6 election.
Ryan referred three times during the debate to television images from Libya and elsewhere in the Arab world in recent weeks that he said showed an unraveling of President Barack Obama's foreign policy.
At the White House, spokesman Jay Carney responded Friday by saying Biden's remarks on Libya correctly reflected that any requests for diplomatic security are handled by the State Department. According to Carney, Obama and Biden were unaware of the specific requests mentioned at the House Oversight Committee hearing.
Biden "certainly was aware" of the congressional testimony when he responded to questions at the debate, which showed that the vice president was referring to himself and Obama in saying that they didn't know about the request for more security, Carney said.
The White House spokesman also repeated earlier assertions that there was no "actual intelligence" beforehand indicating that a terrorist attack on the Benghazi compound was imminent, and noted a formal State Department review was underway.
Secretary of State Hillary Clinton, in a speech on democratic changes in northern Africa, promised the United States would work to bring the Benghazi attackers to justice and that the review she ordered would get to the bottom of what happened.
At the same time, Clinton noted no one expected democratic change in the Arab world to happen quickly or easily. She said the United States must keep up its work promoting democracy, even if that puts diplomats in dangerous and volatile places.
"We will never prevent every act of violence or terrorism or achieve perfect security," Clinton said in the speech at the Center for Strategic and International Studies. "Our people cannot live in bunkers and do their jobs. But it is our solemn responsibility to constantly improve, to reduce the risks our people face and make sure they have the resources they need to do those jobs we expect from them."
At Thursday's debate, Ryan focused on the Libya incident.
The conservative House Budget Chairman accused the administration of failing to properly secure the compound, then giving an incorrect initial explanation for what happened by describing the attack as an anti-American protest, instead of a planned terrorist assault.
Biden smiled and shook his head as Ryan delivered his criticism, then responded that "not a single thing he said was accurate."
However, Biden then denied any knowledge of requests to increase security at the Benghazi compound, saying: "We weren't told they wanted more security there. We did not know they wanted more security."
The Romney campaign blasted Biden for the remark after the debate, releasing a statement that listed a string of media reports pointing out Biden's apparent mistake.
Democratic Rep. Chris Van Hollen of Maryland told CNN on Friday that any information about requests for more security in Benghazi never reached the White House.
"What the vice president is saying is that he and the president didn't know," said Van Hollen, who helped Biden prepare for the debate. "This information had been communicated, at least according to the hearings, to the diplomatic security folks at the State Department and some others. But it wasn't communicated to the president."
Biden headed for Wisconsin on Friday for a campaign event, while Romney and Ryan planned to team up later in the day for a rally in Ohio. With less than four weeks until Election Day, the candidates are focusing on the battleground states still considered up for grabs and vital to each side's chances for victory.
Biden achieved his goal of bringing the fight to his GOP foe in battling Ryan to a draw, boosting the spirits of Democrats disheartened by Obama's lackluster performance in the first presidential debate last week.
Ryan, meanwhile, made a positive impression with his command of both domestic and foreign policy issues that showed him to be a formidable national candidate after a career of local congressional races in his native Wisconsin.
A snap CNN-ORC International poll showed voters who watched the debate narrowly favored Ryan over Biden by 48%-44%, a statistically even result after Romney scored a clear victory over Obama last week in their first of three debates.
Martha Raddatz of ABC News aggressively moderated the debate, challenging both candidates on some claims and moving on to various topics covering both domestic and foreign policy.
Ryan repeatedly said the Obama administration has taken the nation in the wrong direction, asserting it has hindered economic recovery and weakened U.S. influence around the world.
"The choice is clear: a stagnant economy that promotes more government dependency or a dynamic, growing economy that promotes opportunity and jobs," Ryan said. "Mitt Romney and I will not duck the tough issues, and we will not blame others for the next four years."
Biden called several of Ryan's remarks "malarkey" and challenged Americans to trust their common sense when judging proposals by the Republican challengers.
The tax and entitlement reforms proposed by Romney and Ryan would harm the middle class and favor the wealthy, Biden said in seeking to depict Republicans as protectors of the privileged.
"You think these guys are going to go out there and cut those loopholes?" Biden asked about unspecified moves promised by Romney and Ryan to balance broad tax cuts they propose.
On the topic of reforming the Medicare program for senior citizens, which Romney and Ryan seek to partially privatize, Biden referred to a Ryan proposal to provide partial government payment for seniors in the future to buy private health care.
"Folks, use your common sense. Who do you trust on this?" Biden asked, saying Ryan's plan would increase Medicare costs to recipients by $6,000 a year. Ryan disputed the claim, which was based on a proposal that he has since altered.
The debate pitted Biden, 69, and his almost four decades of experience in national politics against the 42-year-old Ryan, a 14-year congressional veteran.
Privately, senior Democrats told CNN they believed a strong showing by Biden could help the Democratic ticket, but wouldn't be enough to erase problems created by Obama's self-admitted bad debate performance against Romney.
Obama and Romney will square off again Tuesday in New York and October 22 in Florida.
Polling after the first presidential debate showed Romney tightening the race nationally and in some of the nine battleground states considered vital to either candidate's chances of garnering the 270 electoral votes needed to win the White House.
"I do think Joe Biden did his boss a lot of good tonight," CNN Senior Political Analyst David Gergen said after Thursday's debate. CNN Chief Political Analyst Gloria Borger said Biden's job "was to right the ship, and he did it."
Both analysts criticized Biden for his tendency to smile and roll his eyes in response to some of Ryan's comments, especially early in the debate, with Gergen saying Ryan won on style but the debate was even with regard to substance.
Biden also was more aggressive in his demeanor, repeatedly cutting off Ryan and sometimes talking at the same time as his rival to challenge specific comments.
At one point, Ryan told Biden that "I know you're under a lot of duress to make up for lost ground, but I think people would be better served if we don't keep interrupting each other."
Biden responded: "Well, don't take all the four minutes then" in reference to how much time the candidates had to respond to a particular question. Overall, Biden spoke for about a minute more than Ryan during the 90-minute-debate at Centre College in Danville, Kentucky.
Ryan repeatedly sought to focus the debate on the Obama-Biden record of the last four years, arguing the administration's policies hindered economic recovery and weakened the nation's standing and influence in the world.
For his part, Biden tried to frame the election as a choice between differing directions for the country by contending policies of the Romney-Ryan ticket would hurt the middle class and move the nation backward on social issues such as gay rights and abortion.
Unlike Obama last week, Biden made sure to mention Romney's controversial comments secretly recorded at a May fundraiser in which the former Massachusetts governor spoke dismissively of 47% of Americans who he said depend on government benefits and don't pay taxes.
In one of his most effective moments, he gave a passionate defense of Americans who participate in the social safety net of entitlement programs and other benefits.
"These people are my mom and dad -- the people I grew up with, my neighbors." Biden said. "They pay more effective tax than Governor Romney pays in his federal income tax. They are elderly people who in fact are living off of Social Security. They are veterans and people fighting in Afghanistan right now who are, quote, 'not paying any tax.'"
In the biggest laugh line of the night, Ryan conceded Romney didn't express the thought exactly as he wanted at the fundraiser, then needled the gaffe-prone Biden by saying: "I think the vice president very well knows that sometimes the words don't come out of your mouth the right way."
Biden immediately responded "but I always say what I mean."
On Iran, widely backed international sanctions pushed by Obama have devastated that country's economy, Biden said. He rejected assertions that Obama failed to work closely with Israeli Prime Minister Benjamin Netanyahu and that the United States lacked commitment to a possible military strike to prevent Iran from becoming capable of developing a nuclear weapon.
"This president doesn't bluff," Biden said.
Ryan, however, insisted that Iran was closer now to having a nuclear weapon than it was four years ago, blaming the administration for allowing that to happen. He bluntly said that Tehran must not be allowed to become a nuclear power.
"This is the world's largest sponsor of terrorism," he said. "And if they get nuclear weapons, other people in the neighborhood will pursue nuclear weapons as well. We can't live with that."
CNN's Ashley Killough and Jessica Yellin contributed to this report.