WASHINGTON (AP)—Two hours after the U.S. Consulate came under attack in Benghazi, Libya, the White House was told that a militant group was claiming responsibility for the violence that killed the U.S. ambassador and three other Americans.

A State Department email sent to intelligence officials and the White House situation room said the Islamist group Ansar al-Sharia claimed responsibility on Facebook and Twitter, and also called for an attack on the U.S. Embassy in Tripoli.

The Obama administration's account of the Benghazi events has become a campaign issue, with Republican challenger Mitt Romney and GOP lawmakers accusing the White House of misleading Americans about the nature of the attack.

The Associated Press and other news organizations obtained the unclassified email and two related emails from government officials who requested anonymity because they were not authorized to speak about them publicly.