Updated

Gabon's government dissolved the country's main opposition party Wednesday, accusing members of high treason after their leader declared himself president of the oil-rich nation, a government minister said.

Opposition leader Andre Mba Obame took the oath of office late Tuesday declaring himself the new leader of Gabon, challenging the authority of President Ali Bongo, the son of Gabon's longtime dictator who died in June 2009 after a 41-year rule.

Obame came in third place in the Central African country's August 2009 elections, which opposition candidates said were fraudulent.

African Union chairman Jean Ping condemned Obame's actions in a statement Wednesday, saying the declaration comes 17 months after a presidential election monitored by international observers.

Obame's announcement "hurts the integrity of legitimate institutions and also endangers the peace, the security and the stability of Gabon," said Ping, who is from Gabon.

The 2009 election was called to replace the late President Omar Bongo. His son Ali was declared the winner with 41.8 percent of the vote, but opposition candidates accused him of vote-rigging. Days of rioting and violence broke out in the southern oil hub of Port Gentil in the former French colony.

Obame was among the country's top three opposition leaders who went into hiding after the elections, saying they feared security forces were trying to kill them.

A spokesman for Obame said at the time that the opposition was considering forming a parallel government.

Late Tuesday at the opposition party headquarters, Obame said it was time for those in Gabon to be directed by someone they truly chose as their leader. He said he would "defend the constitution and the rights of the state."

Obame named a parallel government of 19 ministers, and the group then marched to U.N. headquarters with hundreds of supporters, where they stayed overnight.

The move is likely inspired by events in Ivory Coast, where incumbent leader Laurent Gbagbo has refused to cede power even though the international community recognizes his opponent Alassane Ouattara as president. Ouattara runs a parallel government from a hotel that is being guarded by U.N. peacekeepers.

Jean Francois Ndongou, Gabon's interior minister, said Wednesday that Obame and his co-conspirators had committed high treason, according to a Gabon news website where the government's statement was published.

In the statement, Ndongou said that Obame and his supporters "made the choice to not respect Gabon's constitution."

The government said it has dissolved the National Unity party and "has the right to take other legal and necessary measures relative to this situation."

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Associated Press photographer Joel Bouopda Tatou contributed to this report.