The American embassies in Algeria and Tunisia warned of more protests Wednesday, following attacks by protesters in neighboring Libya in which the U.S. ambassador and three embassy staff were killed.

Ambassador Chris Stevens and the three other Americans died in an attack on the U.S. consulate in Benghazi by armed protesters angry over a film by a California filmmaker that ridiculed Islam's Prophet Muhammad.

In an emergency message, the embassy in Tunis warned Americans to avoid crowded places, saying that even gatherings "intended to be peaceful can turn confrontational and possibly escalate into violence." The embassy in Algiers had similar advice.

The Algiers embassy said unspecified groups were using online social networks to organize demonstrations "to protest a range of issues" there Wednesday. The statement out of Tunis cited "media reports" indicating protests were planned, but said the embassy remained open.

The attack in Libya _ which borders Algeria and Tunisia _ came hours after Egyptian protesters climbed the walls of the U.S. Embassy in Cairo, pulling down the American flag and temporarily replacing it with a black Islamic banner