Washington:
Mitt Romney has accused Vice President Joe Biden of "doubling down on denial" as the White House struggled to combat a growing storm over the attack on the US consulate in Benghazi.
The latest exchanges battered an administration repeatedly thrown onto the defensive by the political reverberations of the attack on September 11 which killed US ambassador to Libya Chris Stevens and three other Americans.
White House spokesman Jay Carney was forced on Friday to clarify remarks by Biden which appeared to contradict evidence that US officials refused extra security for US posts in Libya prior to the Benghazi assault.
"The vice president was speaking about himself and the president and the White House. Obviously he wasn't talking (about) the administration writ large,"Mr Carney said.
Mr Biden said in his campaign debate on Thursday with Mr Romney's running mate Paul Ryan that "we weren't told they wanted more security."
Republican nominee Mr Romney pounced on those remarks as he sought to splinter Mr Obama's reputation as a strong commander-in-chief, 25 days from election day.
"He's doubling down on denial," Mr Romney said in Virginia.
"When the Vice President of the United States directly contradicts the testimony, sworn testimony of State Department officials, American citizens have a right to know just what's going on."
Mr Carney said the vice president was aware of the testimony by US security officials at a congressional hearing on Wednesday that extra protection for the posts had been requested and then denied.
"Nowhere in those four hours of testimony was it suggested that those requests were made essentially to the White House because that is not how this works," Mr Carney said.
The lack of a direct tie so far between Mr Obama and the security situation at the Benghazi post gives the White House a plausible defense, but has not stopped fierce Republican efforts to make the president pay a political price.
Protection issues related to Libya diplomatic posts and elsewhere were dealt with in the appropriate place at the State Department, and not at the White House, Mr Carney said.
State Department spokeswoman Victoria Nuland agreed that generally, such issues were handled inside the State Department.
"I obviously don't have any information to contradict what the vice president said, if that's what you're asking," she told reporters.
The latest developments would be a headache at any time for the White House, but are especially nettlesome given Mr Obama's looming date with voters on November 6.
The Mr Obama campaign hit back, again accusing Mr Romney of politicizing a national security crisis, with spokeswoman Lis Smith saying "the American people deserve more from someone who wants to be Commander-in-Chief."
Secretary of State Hillary Clinton also rode into the fray on Friday amid Republican claims the administration was too slow to brand the attack as terrorism and has frequently changed its story on what happened.
"To this day, to this day, we do not have a complete picture, we do not have all the answers," Ms Clinton said.
She also defended US ambassador to the UN Susan Rice, who had said on the Sunday after the attack that it appeared to be a "spontaneous" protest over an anti-Muslim film made on US soil and posted on YouTube.
Subsequent evidence have suggested there was no major protest outside the consulate, and that the plot was planned by local militants, possibly with help from several outside extremists.
Ms Clinton said that Ms Rice was acting on the same intelligence assessments that every other government official had at the time.
"We can only tell you what we know based on our most current understanding of the attack, and what led up to it. Obviously we will know more as time goes by. And we will know even more than we did hours and days after the attack."
Two US officials testified on Wednesday that requests for extra support for US posts in Tripoli and Benghazi had been refused.
"It was abundantly clear: We were not going to get resources until the aftermath of an incident," regional security officer Eric Nordstrom told the House Oversight and Government Reform Committee hearing.
Mr Nordstrom said he sought to bolster security by asking for 12 more agents, but was told by a State Department regional director that he was asking for the "sun, moon and the stars."
Late Friday, The New York Times reported that in the weeks leading up to the killings of Mr Stevens and the other Americans, US diplomats in Libya indeed sent out a stream of diplomatic cables, warning of a worsening threat from Islamic extremists and requesting that the teams of military personnel and security guards who were already on duty be kept in service.
But the requests, ultimately denied were largely focused on extending the tours of security guards at the US Embassy in Tripoli, not at the diplomatic compound in Benghazi, the paper said.