WASHINGTON - US Secretary of State Hillary Clinton late Tuesday condemned the killing of a US State Department officer in a mob attack on the US consulate in the Libyan city of Benghazi.

Clinton said the US condemned the attack "in the strongest terms," adding that she was "heartbroken by the terrible loss" of the US officer, who was shot dead in Benghazi as angry Muslim protesters burned the US consulate.

The top US diplomat said that there is never any justification of "this vicious behavior as a response to inflammatory material posted on the Internet," stressing that the US "commitment to religious tolerance goes back to the very beginning of our nation."

Clinton, who spoke on phone with Libyan National Congress President Mohammed al-Magariaf to coordinate efforts on protecting Americans in Libya, said the US government is working with partner countries to protect American personnel, missions and citizens worldwide.

In Cairo, Egypt, some Muslim protesters on Tuesday scaled the walls of the US Embassy and replaced the American flag with an Islamic banner.

The anti-American protests in Egypt and Libya, which occurred on the 11th anniversary of the September 11 terror attacks, were both sparked by the posting of video clips on the Internet of an anti-Muslim US movie that insults the Prophet Mohammed.