U.S. Secretary of State Hillary Clinton has praised slain U.S. Ambassador to Libya Christopher Stevens, calling him a “fallen hero” and praising his improvisational style of diplomacy.

She spoke at a ceremony honoring Stevens and others with a Common Ground award, which focuses on conflict resolution, negotiation, and peace building.

In her speech Thursday in Washington, Clinton also said the State Department and the Defense Department are investigating high-threat foreign posts, like Stevens' in Libya, to figure out whether security improvements are needed.

Stevens and three other Americans died on September 11, 2012, in armed attacks on U.S. facilities in Benghazi, Libya.

She said Stevens would never have blamed average Libyans for the extremist attack.

“Chris understood that most people, in Libya or anywhere, reject the extremist arguments that violence and death are the only way to reclaim dignity and achieve justice. He understood; that's why he was in Libya.”

She said the U.S. cannot prevent every act of terrorism, but the nation has a responsibility to constantly reduce the risks its diplomats face. She said U.S. citizens who serve the country overseas “represent the best traditions of a bold and generous nation.”