U.S. citizen killed in Libya, State Department official says

(CNN) -- A U.S. citizen has been shot and killed in the eastern Libyan city of Benghazi, a U.S. State Department official confirmed to CNN Thursday.

The official did not identify the slain citizen. The news came after other reports that gunmen killed an American chemistry teacher working at an international school in the city of Benghazi.

Reuters reported the teacher was slain Thursday, citing medical and security sources.

"He was doing his morning exercise when gunmen just shot him. I don't know why. He was so sweet with everyone," Adel al Mansouri, the director at the school in Benghazi, told Reuters.

It was not immediately clear who was responsible for the killing, Reuters said. CNN is working to get details on the incident.

The U.S. State Department official told CNN that "we offer our condolences to the victim's loved ones."

"We are in contact with the family and are providing all appropriate consular assistance," the official said. "Out of respect for the privacy of those affected, we have no further comment."

Benghazi, Libya's second-largest city, is where militants attacked a U.S. diplomatic mission in September 2012, killing four Americans, including Ambassador Chris Stevens.

More than two years after the fall of Moammar Gadhafi's regime, the Libyan government has been struggling to control the country, which is awash in weapons and armed groups. The security situation has deteriorated over the past year, especially in Benghazi, which was the cradle of the 2011 revolution.

The United States blames one of the armed groups, Islamist militant group Ansar al-Sharia, for the deadly attack on the U.S. mission in Benghazi.