BAMAKO (Reuters) - Malian security forces have arrested at least eight people suspected of plotting an attack in the capital Bamako for the Islamist militant group MUJWA, two senior security sources said on Monday.

Malian officials said the arrests were the first sign that Islamist rebels battling French and African troops for control of Mali's desert north have activated cells in Bamako, which is located in the south.

A high-ranking military officer told Reuters a group made up of 15 people had been trained by al Qaeda-linked MUJWA in Gao, a northern town, and were planning to commit bombings in Bamako when they were arrested.

"The group was dismantled at the beginning of March, but since it was a very sensitive issue we kept it secret (until now)," said the officer, who spoke on condition of anonymity.

He said the group was made up entirely of Malian nationals and that they had been living in Bamako's Banankabougou district near a mosque.

A second security source confirmed arrests had taken place but put the number lower, at eight.

The discrepancy could not be immediately resolved. Malian authorities gave no official comment.

France, assisted by some 2,000 troops from Chad, began a military offensive in January to drive out Islamist fighters who had seized two-thirds of Mali a year earlier.

Hundreds of thousands of Malians have been displaced by fighting and the country's north remains vulnerable to guerrilla-style counter attacks by radical Islamists.

Mali was once viewed as an example of a working democracy in Africa but its north has been plagued by rebellions and become a centre of cross-desert trafficking of drugs, stolen goods and Western hostages.

The U.N. Security Council unanimously approved last Thursday the creation of a 12,600-strong peacekeeping force in Mali starting July 1. It will be supported by the French.

(Reporting by Tiemoko Diallo and Adama Diarra; Writing by Richard Valdmanis; Editing by David Lewis and Mark Heinrich)