Two of the four Americans killed in Tuesday's attack on the US consulate in Libya were former members of the elite Navy SEALs, US officials said.

Secretary of State Hillary Clinton confirmed the identities of the former SEALs as Tyrone Woods and Glen Doherty, praising them as decorated military veterans who "served our country with honor and distinction."

Ambassador Chris Stephens and Sean Smith, an information management officer, also were killed in Tuesday's harrowing assault in the eastern city of Benghazi.

"Our embassies could not carry on our critical work around the world without the service and sacrifice of brave people like Tyrone and Glen," Clinton said in a statement.

Doherty had been working on a mission to track down shoulder-launched surface-to-air missiles in Libya, according to ABC News.

US military and intelligence officials have warned that thousands of the weapons, so-called MANPADs, were unaccounted for after Libya's former dictator, Moamer Kadhafi, fell from power.

The former SEAL described his job in an interview with ABC last month, saying he had traveled across the country chasing leads and then once the weapons were found, his team would destroy them on the spot, the American television network said.

Woods served multiple tours in Iraq and Afghanistan, providing security at US diplomatic posts in Central America and the Middle East.

"He had the hands of a healer as well as the arm of a warrior, earning distinction as a registered nurse and certified paramedic," Clinton said, adding that he is survived by his wife Dorothy and three sons, including Kai, born just a few months ago.

Speaking about Doherty, Clinton said the man who put his life on the line in hotspots throughout the world "died the way he lived -- with selfless honor and unstinting valor."

Doherty reportedly trained as a sniper and medical officer in a seven-year career with the SEALs, before leaving to work at a private security company.

According to an account of the attack from senior officials, Doherty was one of two people who died after staff were evacuated to an annex near the main US consulate building.

With the main building engulfed in flames, the annex then came under sustained gunfire until Libyan forces eventually managed to restore order in the early morning hours.

At least three other Americans were wounded in the attack.

Presidential hopeful Mitt Romney issued a statement earlier Thursday mourning the death of Doherty, who was from Massachusetts, where Romney served as governor.

"Ann and I extend our deepest condolences to the family and friends of Glen Doherty, a native of Winchester, Massachusetts, who was among those killed in Tuesday's assault on our consulate in Libya," his statement said.

"Glen served America with bravery and distinction, and gave his life in an effort to save others."

The US State Department defended its security arrangements at the Benghazi consulate, even though dozens of militants were able to breach the compound and keep US security teams at bay for hours.

"We condemn the attack that took the lives of these heroes in the strongest terms, and we are taking additional steps to safeguard American embassies, consulates, and citizens around the world," Clinton said.

"This violence should shock the conscience of people of all faiths and traditions."

She called for unity in the face of the violence.

"We honor the memory of our fallen colleagues by continuing their work and carrying on the best traditions of a bold and generous nation," the top US diplomat added.