WASHINGTON (Reuters) - Officials at the White House and State Department were advised two hours after attackers assaulted the U.S. diplomatic mission in Benghazi, Libya, on September 11 that an Islamic militant group had claimed credit for the attack, official emails show.

The U.S. Consulate in Benghazi is seen in flames during a protest by an armed group said to have been protesting a film being produced in the United States September 11, 2012. REUTERS/Esam Al-Fetori

The emails, obtained by Reuters from government sources not connected with U.S. spy agencies or the State Department and who requested anonymity, specifically mention that the Libyan group called Ansar al-Sharia had asserted responsibility for the attacks.

The brief emails also show how U.S. diplomats described the attack, even as it was still under way, to Washington.

U.S. Ambassador Christopher Stevens and three other Americans were killed in the Benghazi assault, which President Barack Obama and other U.S. officials ultimately acknowledged was a “terrorist” attack carried out by militants with suspected links to al Qaeda affiliates or sympathizers.

Administration spokesmen, including White House spokesman Jay Carney, citing an unclassified assessment prepared by the CIA, maintained for days that the attacks likely were a spontaneous protest against an anti-Muslim film.

While officials did mention the possible involvement of “extremists,” they did not lay blame on any specific militant groups or possible links to al Qaeda or its affiliates until intelligence officials publicly alleged that on September 28.

There were indications that extremists with possible al Qaeda connections were involved, but also evidence that the attacks could have erupted spontaneously, they said, adding that government experts wanted to be cautious about pointing fingers prematurely.

U.S. intelligence officials have emphasized since shortly after the attack that early intelligence reporting about the attack was mixed.

Spokesmen for the White House and State Department had no immediate response to requests for comments on the emails.

MISSIVES FROM LIBYA

The records obtained by Reuters consist of three emails dispatched by the State Department’s Operations Center to multiple government offices, including addresses at the White House, Pentagon, intelligence community and FBI, on the afternoon of September 11.

The first email, timed at 4:05 p.m. Washington time - or 10:05 p.m. Benghazi time, 20-30 minutes after the attack on the U.S. diplomatic mission allegedly began - carried the subject line “U.S. Diplomatic Mission in Benghazi Under Attack” and the notation “SBU”, meaning “Sensitive But Unclassified.”

The text said the State Department’s regional security office had reported that the diplomatic mission in Benghazi was “under attack. Embassy in Tripoli reports approximately 20 armed people fired shots; explosions have been heard as well.”

The message continued: “Ambassador Stevens, who is currently in Benghazi, and four ... personnel are in the compound safe haven. The 17th of February militia is providing security support.”

A second email, headed “Update 1: U.S. Diplomatic Mission in Benghazi” and timed 4:54 p.m. Washington time, said that the Embassy in Tripoli had reported that “the firing at the U.S. Diplomatic Mission in Benghazi had stopped and the compound had been cleared.” It said a “response team” was at the site attempting to locate missing personnel.

A third email, also marked SBU and sent at 6:07 p.m. Washington time, carried the subject line: “Update 2: Ansar al-Sharia Claims Responsibility for Benghazi Attack.”

The message reported: “Embassy Tripoli reports the group claimed responsibility on Facebook and Twitter and has called for an attack on Embassy Tripoli.”

While some information identifying recipients of this message was redacted from copies of the messages obtained by Reuters, a government source said that one of the addresses to which the message was sent was the White House Situation Room, the president’s secure command post.

Other addressees included intelligence and military units as well as one used by the FBI command center, the source said.

It was not known what other messages were received by agencies in Washington from Libya that day about who might have been behind the attacks.

Intelligence experts caution that initial reports from the scene of any attack or disaster are often inaccurate.

By the morning of September 12, the day after the Benghazi attack, Reuters reported that there were indications that members of both Ansar al-Sharia, a militia based in the Benghazi area, and al Qaeda in the Islamic Maghreb, the North African affiliate of al Qaeda’s faltering central command, may have been involved in organizing the attacks.

One U.S. intelligence official said that during the first classified briefing about Benghazi given to members of Congress, officials “carefully laid out the full range of sparsely available information, relying on the best analysis available at the time.”

The official added, however, that the initial analysis of the attack that was presented to legislators was mixed.

“Briefers said extremists were involved in attacks that appeared spontaneous, there may have been a variety of motivating factors, and possible links to groups such as (al Qaeda in the Islamic Maghreb and Ansar al-Sharia) were being looked at closely,” the official said.