Thousands of people took to the streets of Mali's capital Bamako on Friday to support the West African country's army, which has suffered heavy losses as it struggles to quell a jihadist revolt.

The rally came as a grim discovery in the fragile Sahel nation's conflict-wracked centre illustrated the size of the challenge the army faces.

"Twenty bodies, some abandoned in wells, were found" by soldiers in the village of Peh in the central Mopti region on Wednesday, the government said.

The soldiers were sent to the village after reports of an attack by "unidentified individuals dressed in hunter's clothes," the government said in a statement Friday.

The group "abandoned stolen herds and retreated" when the soldiers arrived, the statement added, without saying how the 20 people died.

A rising jihadist insurgency that spread from the north to the centre of Mali has inflamed tensions between herders and sedentary farmers. Hundreds of lives have been lost in tit-for-tat assaults.

In Bamako, protest organisers said around 15,000 people marched in support of the army. This file photo from September 2018 shows Malian soldiers
In Bamako, protest organisers said around 15,000 people marched in support of the army. This file photo from September 2018 shows Malian soldiers AFP / Michele CATTANI

In Bamako, protest organisers said around 15,000 people marched in support of the army, while the police put the number at "several thousand".

Demonstrators held up signs saying "No embezzlement of our funds" and "Long live FAMA (Malian armed forces)".

Opposition leader Soumaila Cisse said the government had betrayed the army.

"Our soldiers are ill-equipped. We should be fighting for our military to be up to the job," he said, blaming corruption.

Former minister and opposition figure Mohamed Ali Bathily said "the military and ministers who are behind this corruption must be judged".

In the last month around 100 Malian soldiers have been killed in two of the deadliest attacks in the country's history.

The army has been battling to contain the Islamist insurgency despite help from France, African neighbours and the United Nations.