(Bloomberg) -- Sierra Leone’s authorities have said that an attack at the weekend by gunmen on a key army base in the capital, Freetown, was a failed coup.

Thirteen military officers and one civilian, suspected of being involved in the Nov. 26 assault have been arrested, Inspector General of Police William Fayia Sellu, said at a press briefing on Tuesday.

At least 21 people, including 14 of the West African nation’s soldiers had been killed in clashes with the gunmen, Sellu said. Some civilians caught in the crossfire died while three assailants were killed with others still on the run, he said.

“We continue to pursue them outside of Freetown,” Chief of Defense Staff Peter Lavahun said during the briefing. The invasion of two prisons by the gunmen also led to the escape of over 2,200 inmates, of which about 70 have since been captured or returned voluntarily, according to correctional services.

The unrest comes amid increasing tension in the West African nation after President Julius Maada Bio’s disputed reelection in June.

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Some of the group’s leaders fled to the hills on the outskirts of Freetown, where authorities are working to capture them, Information Minister Chernor Bah said on Monday.

“They have been surrounded and we’re very confident that they will be apprehended the next day or so,” he said. “We’re reviewing everything that happened to understand why this breach happened. The president has instructed that additional security measures are put in place.”

The developments in Sierra Leone come after military takeovers in Gabon and Niger this year, and coups in Mali, Guinea, Burkina Faso and Chad over the past three years. The July putsch in Niger, which the Economic Community of West African States is trying to resolve, created a belt of military-run African nations that stretches from the Atlantic Ocean to the Red Sea.

Sierra Leone’s military headquarters lies strategically near the presidential palace and some of the attackers have been identified as former and current members of the security forces, according to Bah. A night curfew will remain in place while the authorities work to determine whether the weekend’s events amount to an attempted putsch, he said.

“We want to make sure that the threshold for an attempted coup is met before signifying it as such,” he said. “Once we have it, we will have to try the people who’ve been arrested.”

The aggression was a plot by “certain individuals” to acquire arms and disturb the peace and constitutional order in the country, the regional bloc known by its acronym Ecowas said in a statement. “Ecowas condemns this act and calls for the arrest and prosecution of all participants in this illegal act.” 

Flights Disrupted

The clashes disrupted flights on Sunday, the civil aviation agency said in a statement. It told airlines to reschedule departing flights for after the curfew is lifted.

Bio, 59, won a second mandate to lead Sierra Leone earlier this year. The results were rejected by the opposition and questioned by international observers including the US, which raised concerns about “irregularities” in the election results.

A retired military officer, Bio briefly led a military junta during an 11-year civil war that ended in 2002. The June election was the fifth since the end of the war, which claimed 50,000 lives and devastated the economy.

--With assistance from Michael Ovaska.

(Recasts with government citing attack as coup attemp.)

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