Economic Community of West African States (ECOWAS) has suspended Mali from the organisation over the ousting of President Ibrahim Boubacar Keita.
President Keita and Prime Minister Boubou Cisse were arrested by rebel soldiers after weeks of unrest.
The Malian president had, on Wednesday, announced his resignation, saying his decision is to avoid bloodshed.
In a statement on Tuesday, ECOWAS asked all its members to close land and air borders to Mali.
It said sanctions will be meted out against “all the putschists and their partners and collaborators”.
In June, opponents asked Keita, who had spent two out of his five-year second term in office, to step down.
A resistance group, M5, also insisted that the constitutional court must be dissolved before peace can return to the country.
The unrest was ticked off by the nullification of results of 31 parliamentary seats in the country’s elections and the awarding of victory to some candidates, which the resistance group said was at the behest of Keita. On July 10, riots led to the killing of some protesters by security agents.