Washington (CNN) - House Speaker John Boehner said Friday that he will form a select committee to investigate the deadly terror attack on the U.S. diplomatic mission in Benghazi in 2012.
The move comes after previously unreleased documents, including an email from a White House national security aide, added to questions about what the Obama administration knew about the armed assault and how it responded in the days after.
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Until now, Boehner resisted calls from House Republicans to establish such a committee, repeatedly pointing to the four House panels already investigating the matter that has become a political flashpoint in the conduct of foreign policy.
But a senior GOP leadership aide said the new email from Ben Rhodes, a document previously not disclosed to Congress that listed talking points on the attack for an administration official, "were the straw that broke the camel's back."
Republicans contend the email, written days after the attack and two months before the 2012 presidential election, proves White House manipulation of the messaging for political purposes, and a cover-up of the fact that Benghazi was, indeed, a terror attack.
"The administration's withholding of documents – emails showing greater White House involvement in misleading the American people – is a flagrant violation of trust and undermines the basic principles of oversight upon which our system of government is built," Boehner said in a statement announcing the new panel.
Separately, House Oversight Committee Chairman Darrell Issa on Friday said he had subpoenaed Secretary of State John Kerry to testify about the development later this month.
Boehner said the select committee would “elevate the investigation to a new level.”
Obama administration officials initially said the attacks stemmed from protests generated by an anti-Muslim film, but evidence emerged that al Qaeda-affiliated terror groups were also involved in the assault.
Rhodes’ email indicates that the goal of the administration's talking points for U.N. Ambassador Susan Rice was to "underscore that these protests are rooted in an Internet video, and not a broader failure of policy."
The email surfaced after Judicial Watch, an outside conservative group, received a response this week to its Freedom of Information Act request for Benghazi materials.
Senior House GOP aides told CNN that the select committee would be led by South Carolina Republican Trey Gowdy, a former prosecutor and member of the Oversight Committee.
But details on how it would work, the kind of investigative powers it would have, and who else would serve on it were being worked out, according to several Republican aides.
Rep. Elijah Cummings, the top Democrat on the Oversight panel, said that committee has already taken the lead on the investigation.
“There is no authority you can give a select committee that Chairman Issa doesn't already have, including the ability to issue unilateral subpoenas to compel any witness or any document,” he said.
Virginia Republican Rep. Frank Wolf introduced a bill to form a select committee three months after the attacks that 190 House GOP members have co-sponsored. Boehner said the House would vote on a measure to create the panel but the timing of the vote is unclear.
The leadership aide, who declined to be identified in order to speak freely about internal talks, explained that "while the existing investigatory committees in the House have full subpoena power, the administration has now demonstrated it is willing to flagrantly defy such subpoena requests, compelling the House to consider taking the strongest actions possible in an effort to ensure Americans have the truth about what happened."
House Democrats contend the continued GOP focus on Benghazi is a motivated by politics.
They said the Rhodes email contains the same type of message that was included in documents already released showing how the administration was interpreting its intelligence on the attacks.
Asked about the new documents on Thursday, House Democratic Leader Nancy Pelosi told reporters, "I haven't seen that but what I will say is diversion, subterfuge. Benghazi, Benghazi, Benghazi – why aren't' we talking about something else?"
Pelosi's spokesman said she has not been contacted by Boehner or anyone else in Republican leadership about the move to form a select committee.
In the Senate, Republicans who have been outspoken on Benghazi called for a joint committee.
“We call on Majority Leader Harry Reid to take similar action and to work with Speaker Boehner to make the select committee a joint effort between the House and Senate. We owe it to the families that lost their loved ones in the Benghazi attack to finally get to the truth,” Sens. Lindsey Graham of South Carolina, Kelly Ayotte of New Hampshire and John McCain of Arizona said in a statement.
Reid was dismissive. “While Republicans try to gin up yet another political food fight, Senate Democrats will remain focused on fostering economic growth for all hard-working Americans,” he said.
CNN’s Ted Barrett contributed to this report.