The Economic Community of West African States in April lifted sanctions against Mali after military leaders ceded authority to civilian authorities.
ECOWAS said it was opposed to plans to replace interim President Dioncounda Traore. His term expires May 22 and authorities have pledged to have new elections. The African bloc, however, said it was concerned about enduring military authority.
"Failure on the part of the (junta) and their civilian allies to clearly reaffirm their commitment to the transitional arrangement in the next few days will be met with the immediate reinstatement of the targeted sanctions," the bloc said in a statement from Abuja.
It added that a standby force was ready for deployment, if requested, to protect humanitarian corridors in the country and to assist in the protection of territorial integrity in Mali.
Coup leaders overthrew the civilian government in March out of frustration with its inability to handle a northern rebellion. Rebel leaders in the north have since declared autonomy for their part of the country.