Guinea's military leaders have freed scores of political prisoners before a meeting of West African leaders to discuss their response to Sunday's coup that ousted President Alpha Conde.

At least 80 political prisoners detained by Conde were released on Tuesday evening. Some had campaigned against his attempt to stay in power for a third term after altering the constitution to permit it, a move opponents said was illegal.

West African countries have threatened sanctions following Conde's overthrow and a regional bloc, the Economic Community of West African States (ECOWAS), was due to convene a virtual summit on Wednesday.

Guinea's main opposition leader said on Tuesday he was open to participating in a transition following a military coup over the weekend, as the officers who seized power consolidated their takeover. 

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Coup leader Mamady Doumbouya, a former officer in the French Foreign Legion, has promised a transitional government of national unity and a "new era for governance and economic development." But he has not yet explained exactly what this will entail, or given a time frame. 

Guinea's main opposition leader, Cellou Dalein Diallo, told Reuters on Tuesday he had not yet been consulted about the transition but was ready to participate. 

"We would send representatives, why not, to participate in the process to bring the country back to constitutional order," said Diallo, a former prime minister who finished runner-up to Conde in three successive elections, most recently last October. 

Sunday's coup, in which Conde and other top politicians were detained or barred from traveling, is the third since April in West and Central Africa, raising concerns about a slide back to military rule in a region that had made strides towards multi-party democracy since the 1990s. 

Conakry was calm for a second day after the military takeover, with some military checkpoints removed. Traffic was normal on Tuesday in the capital's administrative center, the Kaloum peninsula. 

Moving to consolidate their power, the officers that led the coup have installed army officers at the top of Guinea's eight regions and various administrative districts.

(With input from Reuters)