A Senate report has said the FBI, CIA and other intelligence agencies - but not the White House - made major changes in talking points that led to the Obama administration's explanations of the attack on US diplomatic facilities in Benghazi.
The Homeland Security and Governmental Affairs Committee report said on Monday the White House was only responsible for a minor change.
Some Republicans had questioned whether the presidential staff rewrote the talking points for political reasons.
The committee, headed by independent Sen Joe Lieberman and Republican Sen Susan Collins, also said the director of national intelligence has been stonewalling the panel, in holding back a promised timeline of the talking point changes.
US Ambassador to Libya Chris Stevens and three other Americans were killed in the September 11 Libya attack.
The US ambassador to the United Nations, Susan Rice, said she had used the talking points to say in television interviews on September 16 that it may have been a protest that got out of hand.
Rice's incorrect explanation may have cost her a chance to be nominated as the next secretary of state, as Senate Republicans publicly said they would not vote to confirm her.
President Barack Obama instead nominated Democratic Sen John Kerry, chairman of the Senate Foreign Relations Committee, who is expected to win easy confirmation.
The State Department this month acknowledged major weaknesses in security, and errors in judgment exposed in a scathing independent report on the assault.
Two top State officials appealed to Congress to fully fund requests to ensure diplomats and embassies are safe.
Testifying before two congressional committees, senior State Department officials acknowledged that serious management and leadership failures left the diplomatic mission in Benghazi woefully unprepared for the terrorist attack.
The State Department review board's report led four department officials to resign.
The Senate report said that on September 19, eight days after the attack, National Counterterrorism Center Director Matthew Olsen told the Homeland committee that the four Americans died "in the course of a terrorist attack".
The same day, State Department spokeswoman Victoria Nuland said the department stood by the intelligence community's assessment.
The next day, September 20, presidential spokesman Jay Carney said, "It is, I think, self-evident that what happened in Benghazi was a terrorist attack."
Secretary of State Hillary Rodham Clinton also used the words "terrorist attack" on September 21.
Olsen's acknowledgement was important, the report said, because talking points prepared by intelligence officials the previous week had undergone major changes.
A line saying "we know" that individuals associated with al-Qaeda or its affiliates participated in the attacks was changed to say, "There are indications that extremists participated."
The talking points dropped the reference to al-Qaeda and its affiliates altogether. In addition, a reference to "attacks" was changed to "demonstrations".