Dozens of disgruntled soldiers involved in Mali's 2012 coup fired guns in the air at a protest on Monday, wounding and taking hostage a close aide of mutiny leader Amadou Sanogo, military sources said.

The soldiers, based in the garrison town of Kati, near the capital Bamako, were unhappy at not having been promoted alongside colleagues also involved in ousting the president in March last year.

There was confusion over whether Colonel Habib Diallo had been released, with some soldiers inside the camp saying that he had been rushed to hospital for treatment on a bullet wound while others said he remained a hostage.

His condition was unclear and it was not known if he was deliberately targeted or caught by a stray bullet, but military sources told AFP he had been taken hostage shortly before being hit.

"The soldiers who worked with the military junta are unhappy because they have been left behind. Some of them were on the front line but they have not been promoted and they are angry," said a defence ministry official on condition of anonymity.

The official said that "measures are being taken to fully restore order in Kati" and an investigation was underway.

Sanogo led a group of fellow mid-level officers to overthrow then-president Amadou Toumani Toure on March 22 last year, upending what had been considered one of west Africa's flagship democracies.

The mutiny precipitated the fall of northern Mali to Islamist militants linked to Al-Qaeda but a military intervention by French and African troops in January chased the rebels from the region's main cities.

Mali was governed by a transitional administration following the coup until elections saw Ibrahim Boubacar Keita sworn in as the new president in September.

Since August, several authors of the coup or their relatives have been handed promotions, including Sanogo who was elevated from captain to lieutenant-general.

The former junta leader lives and works in Kati but was not present during the protest, a military source said.