Soldiers who staged an uprising in Guinea's capital on Sunday said on state television that they had dissolved the West African nation's government and constitution and closed all land and air borders.
However, the defense ministry said an attack on the presidential palace in Conakry had been repelled.
Fighting broke out near the palace on Sunday morning, with several sources saying an elite national army unit led by a former French legionnaire, Mamady Doumbouya, was behind the unrest. Videos shared on social media on Sunday afternoon, which Reuters could not immediately authenticate, showed President Alpha Conde in a room surrounded by army special forces.
Conde, whose whereabouts were not immediately clear, won a third term in October after changing the constitution to allow him to run again, despite violent protests from the opposition, raising concerns of further political upheavals in a region that has seen coups in Mali and Chad in recent months.
Doumbouya appeared on state television draped in Guinea's national flag and surrounded by eight other armed soldiers, saying his supporters planned to form a transitional government and would give further details later.
"We have dissolved government and institutions," Doumbouya said. "We call our brothers in arms to join the people."
As the Defense Ministry said security forces loyal to Conde had repulsed the attack and were restoring order, people emerged onto the streets during the afternoon to celebrate the uprising's apparent success. A Reuters witness saw pick-up trucks and military vehicles accompanied by motorcyclists and cheering onlookers. "Guinea is free! Bravo," a woman shouted from her balcony.
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The Guinean government has drastically increased and multiplied taxes in recent weeks to replenish state coffers. The price of fuel has increased by 20 percent, causing frustration among many Guineans.
Videos shared on social media had earlier shown military vehicles patrolling Conakry's streets and one military source said the only bridge connecting the mainland to the Kaloum neighbourhood, where the palace and most government ministries are located, had been sealed off.
Guinea has seen sustained economic growth during Conde's decade in power thanks to its bauxite, iron ore, gold and diamond wealth, but few of its citizens have seen the benefits. Critics say the government has used restrictive criminal laws to discourage dissent, while ethnic divisions and endemic graft have sharpened political rivalries.
"While the president was proclaiming everywhere that he wanted to govern differently by annihilating corruption, the embezzlement of public funds increased. The new rich were taunting us," Alassane Diallo, a resident of Conakry, told Reuters.
"It is all this that made it easier for the military."