The ECOWAS military deployment, which comes following a decision by the 15-nation regional bloc at a summit in Ghana's capital Accra on Thursday, did not give details on strength and when the troops will be deployed.
Guinea-Bissau's government said late on Wednesday that attackers in the failed coup attempt on June 14 intended to assassinate the president and were part of a well-funded and tightly planned plot.
It did not say who it believed was behind that attempt, although President Umaro Sissoco Embalo has previously suggested it may be linked to the international drugs trade.
A government said 11 people were killed in the attack, including seven members of the security forces who saved Embalo and his prime minister from death.
Giving new details on the events, it said that unidentified gunmen dressed in civilian clothes burst in on a council of ministers meeting, taking the participants by surprise.
"The aggressors' mode of action clearly reveals that the purpose of the armed attack was the murder of all the authorities present in the council of ministers room," the statement said.
"The robustness of the means and ammunition used demonstrates that this was rigorously planned, relying on funding from sectors with the financial capability to mobilize such an amount of material, logistics and human resources."
One of the attackers - a member of a military police unit - and three civilians were killed along with the seven security personnel, it said. The authorities were still searching for those behind the plot, it said.
Embalo has previously said he did not believe the army was involved in the coup attempt.
The attack was the 10th coup or failed coup in Guinea-Bissau since it gained independence from Portugal in 1974.
ECOWAS deployed a similar mission to the country from 2012 to 2020 after a coup, to help deter the military from intervening in politics and protect political leaders.