BANGUI, Central African Republic — Rebels overthrew Central African Republic’s president of a decade on Sunday, seizing the presidential palace and declaring that the desperately poor country has “opened a new page in its history.” The country’s president fled the capital, while extra French troops moved to secure the airport, officials said.

The rebels’ invasion of the capital came just two months after they had signed a peace agreement that would have let President Francois Bozize serve until 2016. That deal unraveled in recent days, prompting the insurgents’ advance into Bangui and Bozize’s departure to a still unpublicized location.

U.N. Secretary-General Ban Ki-moon condemned the unconstitutional seizure of power and called for the swift restoration of constitutional order, U.N. spokesman Martin Nesirky said.

The U.N. chief appealed for calm and reiterated that the January peace agreements “remain the most viable framework to ensure durable peace and stability in the country,” Nesirky said. Ban also expressed deep concern at reports of serious human rights violations.

Witnesses and an adviser to Bozize said rebel trucks were traveling throughout the town on Sunday hours after the palace was seized. Former colonial power France confirmed the developments, issuing a statement that said French President Francois Hollande “has taken note of the departure of President Francois Bozize.”

“Central African Republic has just opened a new page in its history,” said a communique signed by Justin Kombo Moustapha, secretary-general of the alliance of rebel groups known as Seleka.

“The political committee of the Seleka coalition, made up of Central Africans of all kinds, calls on the population to remain calm and to prepare to welcome the revolutionary forces of Seleka,” it said.

Central African Republic, a nation of 4.5 million, has long been wracked by rebellions and power grabs. Bozize himself took power in 2003 following a rebellion, and his tenure has been marked by conflict with myriad armed groups.

The rebels reached the outskirts of Bangui late Saturday. Heavy gunfire echoed through the city Sunday as the fighters made their way to the presidential palace, though the president was not there at the time.

“Bozize left the city this morning,” said Maximin Olouamat, a Bozize adviser. He declined to say where the president had gone.

The last public news of Bozize’s whereabouts came Friday, when state radio announced he had returned from a visit to South Africa.

Coverseas Worldwide Assistance, a Swiss-based crisis management firm that has contacts on the ground, said it believed Bozize was headed toward neighboring Congo. Bangui is located along the Oubangui River that separates the two countries.

Congolese government spokesman Lambert Mende, however, said he had no knowledge of Bozize crossing into Congo.

U.S. State Department spokeswoman Victoria Nuland said in a statement Sunday that the United States was “deeply concerned about a serious deterioration in the security situation” in Central African Republic.

“We urgently call on the Seleka leadership which has taken control of Bangui to establish law and order in the city and to restore basic services of electricity and water,” the statement said.

Rebels from several armed groups that have long opposed Bozize joined forces in December and began seizing towns across the sparsely populated north. They threatened at the time to march on Bangui, but ultimately halted their advance and agreed to engage in peace talks in Libreville, the capital of Gabon.

A deal was signed Jan. 11 that allowed Bozize to finish his term, which expires in 2016, but the rebels soon began accusing the president of failing to fulfill promises made.

They demanded Bozize send home South African forces who were helping bolster the country’s military. They also sought to integrate some 2,000 rebel fighters into Central African Republic’s armed forces.

Earlier this month, the rebels again took control of two towns and threatening to advance on the capital.

Late Saturday, Bangui was plunged into darkness after fighters cut power to much of the city. State radio went dead, and fearful residents cowered in their homes.

An unspecified number of French citizens have taken refuge in the French Embassy, a French diplomat said on condition of anonymity because he wasn’t authorized to be publicly named according to Foreign Ministry policy. The diplomat said extra French troops were brought in to secure the Bangui airport.

Hundreds of French soldiers already were in the country, some of whom were sent in to protect French interests in the former colony. Bozize had appealed to Hollande for help, but the French president said he would not be protecting the government. Other French soldiers have been providing technical support and helping to train the local army, according to the French defense ministry.

South African Brig. Gen. Xolani Mabanga, the country’s military spokesman, said there had been “intense” fighting this weekend between rebels and South African forces. “Our base was attacked by the rebels as they were advancing toward the capital,” he said.

“We have suffered some casualties,” he said. He declined to provide the number of casualties, pending the outcome of an investigation.

The peace deal also had created a prime minister post, which was given to opposition leader Nicolas Tiangaye, who had been sheltering at a military base for forces from regional neighbors known as FOMAC.

The United States urged the rebels to “provide full support” to Tiangaye, citing the “continued legitimacy” of the peace deal signed in January.

• Hippolyte Maboua & Krista Larson, Associated Press