WASHINGTON — Two more Republican senators expressed deep reservations Wednesday about voting to confirm UN envoy Susan Rice as US secretary of state without more answers about her role in the Benghazi affair.

The embattled Rice met for a second straight day with Republican senators to try to mollify conservatives threatening to block her confirmation if President Barack Obama nominates her to replace Hillary Clinton.

But Senator Susan Collins, a moderate from Maine, joined other Republicans who have sharply criticized Rice for portraying the September 11 attack on the US mission in Libya as stemming from a protest against an anti-Islam film.

"I still have many questions that remain unanswered," said Collins after her hour-long meeting with Rice.

"I continue to be troubled by the fact that the UN ambassador decided to play a political role at the height of a contentious presidential election campaign by agreeing to go on the Sunday shows to present the administration's position," she said.

Rice met separately with Senator Bob Corker, a Republican from Tennessee who expressed outrage at the US administration's actions before and after the attack.

"I could not be more upset with our nation's handling of Benghazi," he said.

Rice steered clear of reporters for a second straight day but later attended President Barack Obama's first cabinet meeting since he won re--election, and got a vote of confidence from her boss.

"Susan Rice is extraordinary, I couldn't be prouder of the job she has done," Obama said, before joining the cabinet in a round of applause for his UN ambassador.

If he nominates Rice, Obama would need 60 votes in the Senate to over-ride Republican blocking tactics on her confirmation.

The Democrats will have 55 senators in their camp when the new Congress convenes in early January, meaning that if Rice were to be confirmed, at least five Republicans would have to vote in her favor.

Collins' remarks echoed those of her more conservative fellow Republican senators -- John McCain, Lindsey Graham and Kelly Ayotte -- who met with Rice on Tuesday and expressed similar reservations.

The controversy centers on Rice's remarks made on Sunday talk shows five days after the assault on the US mission in Benghazi, in which ambassador Chris Stevens and three other Americans were killed.

Using talking points provided by the Central Intelligence Agency, Rice said it was the government's "best assessment" that the assault appeared to have started with a "spontaneous" reaction against an amateur anti-Muslim video.

In a statement after Tuesday's meeting, Rice admitted for the first time that the intelligence community's talking points "were incorrect in a key respect: there was no protest or demonstration in Benghazi."

Collins acknowledged that Rice "made those conflicting assertions (when) there was conflicting evidence, that is true." But the senator said that others, including Libya's de facto head-of-state Mohamed al-Megaryef, knew early on that the attack was a pre-meditated act of terror.

Asked if she would support Rice's nomination if she were picked to be secretary of state, Collins said, "I would need to have additional information before I could support her nomination."

She suggested veteran Senator John Kerry, the powerful chairman of the Foreign Affairs Committee and another potential nominee for the position, would be a safer choice, one who "would be easily confirmed by his colleagues."

After meeting Rice, Corker insisted he would give her "a full hearing" if she is nominated, but he appeared to suggest that he, too, would prefer another nominee.

"I would just ask that the president step back from all of the buzz around this particular situation and take a deep breath and decide who is the best secretary of state for our country at this time when we have so many issues to deal with," Corker said.

Clinton is set to step down as the top US diplomat early next year, and Rice is widely touted as the favorite to be nominated for the post.