DAKAR and LONDON -- A group of soldiers declared a coup d'état in Gabon on Wednesday, claiming to have seized power from a president whose family has ruled the oil-rich Central African nation for decades.

The military junta made the announcement on state television hours after Gabonese President Ali Bongo Ondimba won reelection for a third term in a vote that was criticized by international observers. A dozen uniformed soldiers, who introduced themselves as members of the Committee of Transition and the Restoration of Institutions, described the election as fraudulent and said the results were "canceled," all borders "closed until further notice" and state institutions "dissolved."

"Our beautiful country, Gabon, has always been a haven of peace. Today, the country is going through a serious institutional, political, economic and social crisis," the soldiers said in the televised statement. "In addition, irresponsible, unpredictable governance has led to a steady deterioration in social cohesion, threatening to drive the country into chaos. We call for calm and serenity among the population, the communities of sister countries settled in Gabon, and Gabonese living abroad. We reaffirm our commitment to respecting Gabon's commitments to the national and international community."

The coup leaders later issued another statement saying the president was under house arrest in his residence in the Gabonese capital of Libreville. Bongo, 64, became president of Gabon in 2009 following the death of his father, who had ruled since 1967.

Throngs of people took to the streets in Libreville on Wednesday to celebrate the apparent coup.

Sources told ABC News that internet service in Gabon was restored nationwide following the military takeover.

The U.S. Embassy in Libreville issued a security alert on Wednesday saying it "has received reports the borders and airport are currently closed and commercial flights to and from Libreville will reportedly be suspended until further notice." U.S. citizens in the Gabonese capital were advised "to shelter in place, limit unnecessary movements around town, and continue to avoid transiting the downtown and Presidential Palace area."

If successful, Gabon's coup would be the eighth to occur in West and Central Africa since 2020. It comes about a month after a military junta in Niger ousted the West African nation's democratically elected government. Both Niger and Gabon have close ties to France, their former colonizer.

Speaking to reporters in Paris on Wednesday, a French government spokesperson condemned the coup attempt in Gabon and said the government was following the situation closely.

The United States is still evaluating the situation on the ground in Gabon and American diplomats at the embassy there are conferring with consular officials from other likeminded countries, a senior official with the U.S. Department of State told ABC News on Wednesday.

All staff members of the U.S. embassy in Libreville are accounted for, according to the official.

Some gunshots were fired in the Gabonese capital as the coup attempt unfolded earlier Wednesday, but as a means of intimidation rather than direct violence, the official claimed, saying the situation is still developing.

The African Union, a bloc consisting of 55 member states located on the African continent, including Gabon, issued a statement Wednesday "strongly" condemning the attempted coup in Gabon and calling for "a rapid return to democratic constitutional order in the country."

Gabon, home to more than 2 million people, is located on the western coast of Central Africa, sharing borders with Equatorial Guinea, Cameroon and the Republic of Congo. The country is a member of OPEC, with a production of 181,000 barrels of crude per day.

-ABC News' Shannon Crawford contributed to this report.