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Leading congressional lawmakers applied new pressure to the Obama administration Thursday for information on the Libya terror attack, after emails published this week showed top officials being told within hours that a local militant group had claimed responsibility.

Republicans are using the alert on Sept. 11, contained in State Department emails, to challenge initial claims by administration officials that attackers were reacting to protests over an anti-Islam film.

House Speaker John Boehner, in a lengthy letter sent to President Obama on Thursday, called on the president to "explain to the American people" what happened.

"The American public is increasingly reading information contradicting early accounts by your administration of the causes of the events of the day," Boehner said. "In the absence of your direct engagement to clarify these concerns, the public's frustration and confusion is likely to discredit efforts to achieve our shared goals of justice and accountability for the direct assault on American interests and the deaths of four public servants."

He called the latest information "deeply troubling" to lawmakers who attended a briefing after the attack, "as there are perceived inconsistencies between what they learned during the briefing and the now widely available documentation regarding what was known at the time of the attack."

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    Boehner's letter came as the Senate intelligence committee announced it would hold a closed oversight hearing on Nov. 15, "with additional hearings to follow."

    Rep. Darrell Issa, R-Calif., chairman of the House oversight committee, and Rep. Jason Chaffetz, R-Utah, also wrote a letter to Obama on Thursday asking about the newly disclosed emails.

    "The committee is concerned that this important report in an inter-agency dialogue appears to have been discarded in favor of different conclusions that have since been found to be false," they wrote. "We request your assistance in understanding why this report was disregarded for weeks in favor of flawed conclusions about a spontaneous protest."

    The emails show top officials were alerted to militant group Ansar al-Sharia in Benghazi claiming responsibility on Facebook and Twitter shortly after the strike began. The group has since denied carrying out the attack - though it is still suspected of being behind strike.
    Secretary of State Hillary Clinton downplayed those emails on Wednesday.

    "Posting something on Facebook is not in and of itself evidence," Clinton said. "And I think it just underscores how fluid the reporting was at the time and continued for some time to be."

    Though the emails are just one piece of the puzzle, they reveal some of the most detailed information yet about what officials were saying to each other in the initial hours after the attack. And they again raise questions about why U.S. Ambassador to the U.N. Susan Rice, apparently based on intelligence assessments, would claim five days after the attack that it was a "spontaneous" reaction to protests over an anti-Islam film.

    "It is clear that information now in the public domain contradicts how you and senior administration officials consistently described the cause and nature of the terrorist attack in the days and weeks immediately following.  Why did the administration fail to account for facts that were known at the time?" Boehner wrote in his letter.

    Boehner also raised concerns about documented "security problems" in the country before the attack and asked when was the last time Obama was briefed by Stevens. Further, he asked for more information on what military options were available during the attack and "why it appears assets were not allowed to be pre-positioned, let alone utilized."

    To that point, Defense Secretary Leon Panetta said the military "had forces in place" to respond but did not want to intervene without a clear picture of what was happening on the ground.

    "I'm sure there's going to be -- there's a lot of Monday morning quarterbacking going on here," he said. "But the basic principle here ... is that you don't deploy forces into harm's way without knowing what's going on."

    Meanwhile, more signs of extremist involvement in the attack continue to surface. Fox News was told that the suspect currently in Tunisian custody - Ali Ani al-Harzi - has a brother who was a jihadist with Al Qaeda in Iraq. Separately, among the list of suspects being reviewed by the FBI and intelligence community is at least one individual who is believed to have fought for Al Qaeda in Iraq and also participated in the consulate attack.

    These links between Benghazi and AQI are described as "limited" at this point in the investigation.

    Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee, also told Fox News that he believes a second attack on the U.S. Embassy in Tunisia on Sept. 14 was the work of Ansar al-Sharia as well.

    "Clearly a jihadist group. I believe it will be determined probably Ansar al-Sharia," Rogers said, adding he believes the group was emboldened by its success in Benghazi and struck again.

    "Clearly they decided to take advantage of the momentum of 9/11 -- clearly that was their case and they had moderate success," he said.

    Fox News' Catherine Herridge contributed to this report.