Rebels penetrated the capital of Chad on Saturday, clashing with government troops and moving toward the presidential palace after a three-day advance through the central African nation, a French military spokesman and witnesses said. Col. Thierry Burkhard said groups of rebels gathered outside the capital, N'Djamena, overnight, before about 1,000-1,500 fighters entered the city early Saturday. The French and American governments told their citizens to assemble in secure locations as witnesses reported looting and gunfire near government buildings. France's embassy in Chad sent messages over Radio France Internationale to tell citizens to head to the Lycee Francais high school and two other locations in N'Djamena a French diplomatic official said on condition of anonymity. France's military has about 1,400 personnel in Chad, about 1,200 of those in the capital. William Spindler, a spokesman for the U.N. High Commissioner for Refugees, and said 51 U.N. staff were evacuated from N'Djamena to Cameroon overnight. The agency still had eight staff in N'Djamena, Spindler said. Ibni Oumar Mahamat Saleh, the coordinator of Chad's main non-armed opposition alliance, said gunfire began at about 8 a.m. and ended about two hours later. "We do not know what is happening ... Civilians are in the streets. They are watching what is happening," he said. "The radio has gone off air. Television here only broadcasts in the evening so we will know later whether it is off air," Saleh told The Associated Press. Chad, a former French colony, has been convulsed by civil wars and invasions since independence from France in 1960, and the recent discovery of oil has only increased the intensity of the struggle for power in the largely desert country. The most recent series of rebellions began in 2005 in the country's east, occurring at the same time as the conflict in neighboring Sudan's western region of Darfur saw a rise in violence. One Chadian rebel group launched a failed assault on N'Djamena, in April 2006. Deby himself came to power at the head of a rebellion in 1990; he won elections since, but none of the votes were deemed free or fair. He brought a semblance of peace after three decades of civil war and an invasion by Libya, but became increasingly isolated and members of his own family have joined Chad's latest rebellion. U.N. officials estimate that around 3 million people have been uprooted by conflicts in the region, including the fighting in western Sudan's Darfur region, which borders Chad, and rebellions in Central African Republic.