FILE - In this Jan. 8, 2013 photo, Francois Bozize, president of the Central African Republic, speaks to the media in front of a map of the country in the colors of its flag, at the presidential palace in Bangui, Central African Republic. After years as a high-ranking military officer, Bozize launched a rebellion in 2001, taking Bangui two years later, when the then-president was out of the country. (AP Photo/Ben Curtis, File) BANGUI, Central African Republic (AP) - Hundreds of rebels penetrated the capital of Central African Republic on Saturday, posing the gravest threat to President Francois Bozize's government in a decade. In at least one part of the city, the insurgents faced resistance and were battling their way through, a group monitoring the situation said. The capital of this desperately poor nation was plunged into darkness after fighters cut power to much of the city. State radio went dead, and fearful residents cowered in their homes Saturday night. The rebels, who signed a peace agreement in January that was to allow Bozize to stay in power until 2016, have been threatening to overthrow the president unless he meets their demands. The rebels come from several different armed groups that have long challenged the government and have an array of grievances and demands. They are now accusing Bozize of failing to abide by the terms of the latest deal signed two months ago, with the help of mediators from neighboring countries. "For us, there is no other solution than the departure of Francois Bozize," Eric Massi, a rebel spokesman, said from Paris by telephone late Saturday. Massi confirmed that the rebel forces had entered Bangui and were continuing their advance into the capital in an effort to secure the city. Rebel fighters had rapidly seized a dozen towns in December and January but never entered the capital before agreeing to the negotiations that led to the failed January peace accord. Guy Moussa, who lives in the PK12 neighborhood on the north side of the city, told The Associated Press that hundreds of rebels were seen entering the city around 6 p.m. Coverseas Worldwide Assistance, a Swiss-based crisis management firm with contacts on the ground, said that rebels, known as Seleka, had split into three columns. One had set up a base in PK12, while a second headed further into Bangui and met no resistance. A third column entered Bangui from the west, where the rebels faced resistance and combat was ongoing. Earlier in the afternoon, non-essential United Nations personnel taking a bus to the airport had been stopped by a group of angry youths. No one leaves this country. You will stay here. If we die, we all die together," the youths shouted, according to U.N. employee Debonheur Deotar. The growing unrest is the latest threat to the stability of Central African Republic, a nation of 4.5 million that has long been wracked by rebellions and power grabs. The president himself took power in 2003 following a rebellion, and his tenure has been marked by conflict with myriad armed groups. Bozize's whereabouts late Saturday were not immediately known. On Friday, state radio announced that he had returned from South Africa where he was meeting with that country's president, Jacob Zuma. Massi, the rebel spokesman, said Bozize was believed to be sheltering at the South African Embassy in Bangui. South Africa has sent troops and equipment to support Central African Republic forces. The rebels insist the foreign troops leave, and, as part of their demands, they want their own fighters integrated into the national army. On Friday, the rebels seized Damara, which had been the boundary line drawn up by regional forces before the January peace accord was signed. The move marked a serious escalation by the rebels, who went on to take the town of Bossembele early Saturday, said military spokesman Lt. Evrard Tekremoyen. The insurgents then drove to the neighboring town of Boali and took control of three power plants that serve the town and the capital, residents said. The rebels also cut off the electrical grid, plunging some of Bangui into darkness, Elisabeth Kofio, the director of Central African Republic Energy, said on the radio. Earlier in the week, Bozize had offered to release some political prisoners, but the rebels said the gestures were too little, too late. Larson reported from Dakar, Senegal.